Vedic Rudra Vs Shiva & Śankara? Is Śiva an adjective or title?

The title Śiva is used for Rudra in various hymns denoting his “Very Nature”, meaning anything about Rudra is Śiva, and not just that, if Śiva is just an adjective then Rudra is the “highest Śiva”. What tops this list are 3 statements of Veda that are beyond mere deductions. So let’s trace our steps back from Krishna Yajur to Shukla Yajur, finally to Rig Veda. Two are from Yajur Veda Taittirīya Saṃhitā which says:

या ते रुद्र शिवा तनूः शिवा विश्वाह भेषजी | शिवा रुद्रस्य भेषजी तया नोमृड जीवसे 4.5.10.2
“yate Rudra Śivā tanuhu Śivā Vishvaha Bheshaji | Śivā Rudrasya Bheshaji “

Oh Rudra you are of Śiva (auspicious) body/form. As Śivā to your the medicine/cure (भेष॒जी) to all entirety, you are eternal cure to all worldly ailments (विश्वाहभेषजी ) With that (तया) auspicious form (शिवा) you are the cure to our crying/suffering (रुद्रस्य) (samsara/avidya) medicine (भेषजी) is the relief to us all (न) jivas (जीवसे all living entities) comfort/solace (मृड).
Please note: नो मृड जी॒वसे᳚ : can also interpreted as “save our lives (जी॒वसे᳚) away (नो ) from death (मृड)”

Please note: Same hymn has its source in Sukla Yajur Veda Vājasaneyi Saṃhitā 16.49.
Note: Here Śivā is not just auspiciousness (Śiva – Adjective) nor is it limited to feminine. Whenever there is an emphasis on ā it represents a Collective, hence its a noun. This collective is the unified presence of both masculine and feminine.

नमः शिवाय च शिवतराय च | “Oṃ namaḥ śivāya cha śivātarayācha” 4.5.8
Salutations to that Śiva (the auspicious one), who is The most auspicious one (शिवतराय).

Kṛṣṇa Yajur Veda Taittirīya Saṃhitā 4.5

_{Note: Śiva, Śivo, Śive, Śivam, Śivatvam & Śivā
Śiva = Auspiciousness, Bliss, contradiction-absence (Adjective)
Śive = With Auspicious or of being Auspicious (Verb)
Śivo = That Auspiciousness (Pronoun pointing to an Adjective)
Śivam / Śivatvam = of the Nature of being Auspicious (a Noun defined with an adjective)
Śivā = Auspicious pair (Collective Noun)}

So, Rudra has a “Śivā form” which is an auspicious form, the same Rudra is Ugra and Aghora (fierce). As Śivā, He is the cure to all living, and as Rudra, He is the enforcer of cosmic Law (Rta). Not only that he is Śiva, He is the highest Śiva (most auspicious). So Rudra’s very nature is Śiva. So, anything and everything about Rudra is Śiva.

If everything about Rudra is Śiva, What about his fierce weapons?

यात इषुः शिवतमा शिवं बभूव तेधनुः । शिवा शरव्या या तव तया नोरुद्र मृडय ॥
Ya+ta Ishu shivatama shivam babhuva te dhanuh | Śiva sharavya ya tava taya no Rudra mrudaya
Those arrows (इषु) are of Śiva+atvam (are auspicious), and that bow is also Śivam, that quiver is also Śiva.

शिवां गिरित्र तां कुरु मा हिसीः पुरुषं जगत् ||
Śivam giritra tam Kuru ma higmsih purusham jagat
Oh Dweller of the mountains, let those arrows be Śiva towards all beings of reality.

Kṛṣṇa Yajur Veda Taittirīya Saṃhitā 4.5

Rudra is gātha-patim, meaning the resort to all hymns/songs, and also medha-patim, the resort of Yajñá/Sacrifice/Oblations, so how should our oblations to Rudra be?

शिवेन वचसा त्वा गिरिशाच्छा वदामसि ।
Śivena vachasa tva giri shacchavadamasi||
With auspicious words, we appeal to your oh dweller or mountains.

Kṛṣṇa Yajur Veda Taittirīya Saṃhitā 4.5

Can we move back into earlier Vedas and give a definitive claim that Śiva is also a name? Shukla Yajur Veda Vajasneyi Saṃhitā 3.63 says:

“Śivo nāmāsi svadhiṣṭhite pitha namaste asthu”
my salutations to the one named Śiva (the auspicious and gracious one) the all-knowing father, harm us not”.

Shukla Yajur Veda Vajasn

What about Rig Veda, does it say Who is Śiva?

स्तोमं वो अद्य रुद्राय शिक्वसे क्षयद्वीराय नमसा दिदिष्टन येभिः शिवः स्ववाँ॑ एवयावभिर्दिवः सिषक्ति स्वयशा निकामभिः
We sing our devotional praise (स्तोमं) for you (वो) oh Rudra (रुद्राय) we show/shower (दिदिष्टन) our salutations (नमसा) oh intelligent one (शिक्व) oh ruler of men/beings/heroes/brace (क्षयद्वीरा), who is Śiva (येभिः – शिवः) with our devotion may we unite with you (सिषक्ति) oh majestic glorious one (स्वयशा) our protector (स्ववान् / स्ववाँ॑), who is swift in delivering that protection (एवयाव = swift, एवयावभिर्दिवः swift-moving/walking), oh granted of our wishes (निकाम).

Rig Veda 10.92.9

Till now we covered Saṃhitās across Vedic Shakas, now let’s go to the most famous hymn from two Vedic Āraṇyakas:

भवाय नमः । शर्वाय नमः । शिवाय नमः । ज्वलाय नमः । आत्माय नमः । परमाय नमः । 10.16.34.16
Bhavaya Namaha | Sharvaya Namaha | Śivaya Namaha | Jwalaya Namaha | Atmaya Namaha | Paramaya Namaha |

ईशानः सर्व विद्यानामीश्वरः सर्वभूतानां ब्रह्माधिपतिर्ब्रह्मणोऽधिपतिर्ब्रह्मा शिवो मे अस्तु सदाशिवोम् ॥10.21.39.21
īśānassarva vidyānām īśvaras sarva bhūtānām brahmādhipatir brahmaṇo’dhipatir brahmā śivo me astu sadāśivom
As īśāna (5th facet of Sadaśiva) you are the holder of all knowledge (Vid), As īśvara you are the sovereign Authority towards all beings (सर्व+भूतानां ), you are the overlord of Brahma (wisdom and its creative principle), and overlord receiver of all prayers (ब्रह्मकार) of all, He is the ever expanding Supreme consciousness (र्ब्रह्मा) which is nothing but auspicious (शिवो ) well that is (मे +अस्तु) is the eternal/infinite auspiciousness (सदा+शिवोम्).

“nama̍ste astu bhagavan viśveśva̱rayā mahādevāya tryaṁbakāya tripurāntakāya trikalāgni-kālāya kālāgnirudrāya nīlakaṇṭhāya mrutyuṁjayāya sarveśvarāya śankaraya sadāśivāya śrīmanmahādevāya namaḥ. Kṛṣṇa Yajur Vedā 4.5
“My Salutations unto the Divine Authority over all that pervades, the principle (maha) of all divine, the one with three eyes, the one who ended the Tripurasuras the 3 celestical worlds, he is the 3 fires which blaze at all times, this is the fire that devours time, the one with blue neck which holds the anti-creation element, by this He is beyond death, he is the authority over the entirity, the one who bestows bliss, as he is forever auspicious along with his śakti, he the prosporous highest of divine my homage

Kṛṣṇa Yajur Veda 4.5 / Taittirīya Āraṇyaka 10.21.39.21 /10.16.34.16

So, Śiva is not just a temporary state or form, but he is sadāśivāya, meaning forever Śiva. But is it just the Rishis who addressed this way? Did other divine aspects or Devas address so?

Wandering Rudra in the heavenly realm (svargaṃ lokaṃ) with a sun-like luster/brilliance (ādityavarṇaṃ). The Devas who ascended to the heavenly realm saw and sought Rudra as to who he was (.abruvan: ko .asīti). I am Rudra (ahaṃ rudro), I am Indra (aham indro), I am the Āditya (aham indro, aham ādityo), I am divine brilliance the encompasses entirety ( ahaṃ sarvasyāvayā haraso divyasyeti). The Devas claimed no offering to Rudra. He Roared fiercely towards them (rudratvam). The devas realized this and addressed him with due reverence by calling him Bhava. They said Bhava the entirety is thy Sarva. Because they said you are all this that revealed Śarva’s [prowess] as an archer. Because he then became favorable that is Śiva’s benevolence.

Caraka Katha Āraṇyaka 2.100/101

Time to compare all the above with Primary Upaniṣhads:

यदाऽतमस्तान्न दिवा न रात्रिर्न सन्न चासच्छिव एव केवलः। तदक्षरं तत्सवितुर्वरेण्यं प्रज्ञा च तस्मात्प्रसृता पुराणी॥
यदा अतमः तत् न दिवा न रात्रि न सत् न च असत्। केवलः शिवः एव तत् अक्षरम् तत् सवितुः वरेण्यम्। तस्मात् पुराणी प्रज्ञा प्रसृता॥ Svetasvatara Upaniṣhad 4.18
When there is no darkness, not day (न दिवा) nor night (न रात्रि), not being (न सत्) nor non-being/no basis for anything (न च असत्), immutable/ unchangeable/ unblemishable/ unaltered (तत् अक्षरम्), that the supreme light of the Creating Sun (तत् सवितुः वरेण्यम्) as its source (तस्मात्) all that is to be known and ancient (पुराणी प्रज्ञा) has come to be (प्रसृता) from that absolute singularity that is Śiva (एव केवलः शिवः)

Svetasvatara Upaniṣhad 4.18

Did the Primary Upaniṣhads actually use the term Śiva both as a name and as a form?

अणोरणीयानहमेव तद्वन्महानहं विश्वमहं विचित्रम् ।पुरातनोऽहं पुरुषोऽहमीशो हिरण्मयोऽहं शिवरूपमस्मि ॥ 20
I am (अहम-एव– तद्व) the atomic (अणर) and smaller than that (अणीयान) I am also (अहं) the vastness/greatness (महान) I am the Vishvam the created universe (विश्वम) and I am mystical and astonishing (विचित्रम्) | I am the most ancient (पुरातन – अहं), I am the Purusha/the consciousness in all beings (पुरुष) and I am the Isha the Sole Ruler (ईशा), I am the brilliance (हिरण्मयो), and my nature and form is Śiva (शिव-रूपम-अस्मि).

भोक्ता भोगश्च यद्भवेत् । तेभ्यो विलक्षणः साक्षी चिन्मात्रोऽहं सदाशिवः ॥ 18
I am the one who is the experiencer (भोक्ता) and the cause of that experience (भोगश्च यद्- भवेत्) | I am mysterious and facinating (विलक्षण) and also the witness to it (साक्षी), I am the consciousness and intelligence (चिन्मात्र) I am forever Śiva सदाशिवः)

स ब्रह्मा स शिवः सेन्द्रः सोऽक्षरः परमः स्वराट् । स एव विष्णुः स प्राणः स कालोऽग्निः स चन्द्रमाः ॥ 8
I am Brahma, I am Siva, Indra, I am undecay (अक्षर), I am the highest (परम), I am the brilliance (स्वराट्) |I am that Vishnu, I am the Prana, I am time, fire and moon (विष्णु, प्राण, काल, चन्द्रमा)

Kaivalya Upaniṣhad

Following is a statement of Kṣemarāja, the brilliant student of Abhinavagupta belonging to the Trantra/Yoga branch of literature, he says Rudra as samastarugdrāvi:

Bhairava or Śiva is called Rudra, because ru stands for ruk (disease), and dra stands for drāvi (melter, dissolved). samastarugdrāvi – Rudra is one who dissolves all the ills (of life).

Vijñānabhairava Tantra or Divine Consciousness, book by Jaideva Singh p3.

Let’s finally close this with the purification hymns sung to invoke Rudra into various parts of our body and become a Rudra oneself. This process is called Nyāsa performed before Sri Rudram chanting. The very first hymn used to enter into mediation (dhyana) says:

ॐ अथात्मानगं शिवात्मनाग श्री रुद्ररूप-ध्यायेत|
शुद्धस्फटिक संकाशं त्रिनेत्रं पंच वक्त्रकम | गंगाधरम दशभुजम सर्वभरण भूषितम
नीलग्रीवं शशांककं नाग यान्नोप वितीनम | व्याघ्र चर्मोत्तरीयं च वरेण्यमभाय प्रदम
वृष स्कंध समरूढम उमा देहार्थ धारीणम | अमृतेनाप्लुतं शांतम दिव्यभोग समन्वयम
दिग्देवता समययुक्तं सुरासुर नमस्कारम | नित्यं च शाश्वतम शुद्धम ध्रुवमक्षरमव्ययम्
सर्व व्यापिन-मीशानम रुद्रं वै विश्वरूपिनम | एवं ध्यात्वा द्विज: सम्यक ततो यज्ञमारभे

Om Meditate on the Rudra form who is the Atman (self) of all and who is the very Śiva atma.
Who appears (संकाशं) a pure crystal (शुद्ध-स्फटिक ) with three eyes (त्रिनेत्रं ) with five heads (पंच वक्त्रकम ) | who hold the Great Ganga (गंगाधरम ) with ten hands (दशभुजम ) with entirity as his ornaments (सर्वभरण भूषितम), with blue neck (नीलग्रीवं ) and a cresent moon (शशांककं ) and snake as his sacred thread (नाग यान्नोप वितीनम) wearing an animal hide (व्याघ्र चर्मोत्तरीयं) with His very essence is bliss (वरेण्यमभाय प्रदम ), his ride is the bull (वृष स्कंध समरूढम ), the every auspecious Uma is his very body (उमा देहार्थ धारीणम ) dripping with elixer (अमृतेनाप्लुतं) ever in peace and bliss (शांतम ) surrounded with all weath and riches and comforts (दिव्यभोग समन्वयम) with Dvinities on all sides (दिग्देवता ) with oblations from both Asuras and Devatas alike (सुरासुर नमस्कारम) He is forever eternal (नित्यं च शाश्वतम) pure, stationed/unmoving (ध्रुव-मक्षर-मव्ययम्), He encompasses everything (सर्व व्यापिन) He is Rudra of the cosmic form (रुद्रं वै विश्वरूपिनम), upon this one meditate perfectly (ध्यात्वा सम्यक ) as oneself the sacrifice (ततो यज्ञमारभे)

Sri Rudram LaghuNyāsam

It’s obvious at this point who is Rudra and what is Śiva. Yet our mind dwells on the so-called Śankara of both Itihāsas and Puráńas. The one with a blue neck, matted hair, wearing deerskin and snakes, holding a trident (trishuula) the resident of Kashi/Varanasi, a dweller of mountains and married to the daughter of those mountains (Uma). Are they all the same? Does Vedas declare that Rudra’s auspicious side is Shiva or Śankara or Dakshina Murti?

Who is Sankara?

For our second question, the answer is quite simple. The Vedas focused on the cosmic phenomenon called Ṛta and revolved around Yajñá, and used the titles that suit the nature and cosmic principle in the discussion. Hence, for Vedas, the one who is the lord of all sacrifice and all hymns should be the one to enforce the sanctity of Yajna and the sanctity of mantras (Vak). This being should be fierce yet auspicious. This being should be nameless and unknown and should devour our papa (sins), our mistakes, our wrongdoings, and our leftovers. This being should be feared yet loved by both Rishis and commoners. That entity is RUDRA.
However, the Puráńas, and Itihāsa are devotion centric, and focused on the benevolent side of Rudra-Śiva, his nourishing, healing, protecting, unconditional and blissful nature – and Śiva (the Auspiciousness One) was the most suited title.

Yet one should notice that in Itihāsa, more than the title Śiva, all 8 names (Astamurthi) are used based on the context of narration. Among them, the most used and famously known titles are Adi Yogi who is called Dakshina Murti and in this state, he is the auspicious side of Rudra who creates auspiciousness for us hence the title Samkara/Shankara (नमः शङ्क॒राय TS4.5.8) and Maheśvara. One must ask, is this an assumed conclusion, or did the sages conclude that the auspicious side of Rudra is Dakshina Murti? Let’s start with the famous Shiva Sankalpa Suktam of Rig Veda Baskala Khila and also present in the Sukla Yajur Veda:

कैलासशिखरे रम्ये शंकरस्य शुभे गृहे । देवतास्तत्र मोदन्ति तन्मे मनः शिवसंकल्पमस्तु ।। Rig Veda 24
The splendid (रम्ये) summits (शिखर) of mount Kailash (कैलास) is the auspicious residence (शुभे गृहे) of the Lord Shankara (शंकरस्य). All divinities (देवता) are stationed (स्तत्र) delighted in His presence (मोदन) with the inner self absorbed into Him (तन्मे मनः) may that be my auspicious resolve – many my resolve be of Śiva (शिव-संकल्प-मस्तु).

Rig Veda Bhaskāla Śākhā Khilani 33 (Śivā Sankalpa Sukta)

Well, let’s ask the conclusion of Vedas, the Vedānta (Veda+Anta = End of Vedas):

तमादिमध्यान्तविहीनमेकं विभुं चिदानन्दमरूपमद्भुतम् । तथादि उमासहायं परमेश्वरं प्रभुं त्रिलोचनं नीलकण्ठं प्रशान्तम् । ध्यात्वा मुनिर्गच्छति भूतयोनिं समस्तसाक्षिं तमसः परस्तात् ॥ 6
Meditate on me, I am without beginning or middle or end (तम अदि-मध्य-अन्त) the one singularity (ऐकं) the one almighty/all-pervading (विभुं) the one who is the personification of eternal bliss of Cit (चिदानन्दम -रूपम) who is astonishing/mystical (अद्भुतम्), the consort of the ever auspicious Uma (उमा सहायं ) who is eternal self-governing ruler (परमेश्वरं प्रभुं) with three eyes (त्रिलोचनं) and a blue neck (नीलकण्ठं) who is forever peaceful in His own-self (प्रशान्तम्) mediate your thoughts on this form (ध्यात्वा), a true sage (मुनिर्गच्छति) will reach/realize the source and womb of all beings (भूत-योनिं) and the only witness to all (समस्त-साक्षिं) and beyond all unmanifest (तमसः परस्तात्). 

Kaivalya Upaniṣhad 6

What about Rudra/Śiva being the Dakshina-facing Deity?

कश्चित् भीरुः अजात इति एवं प्रपद्यते। हे रुद्र यत् ते दक्षिणं मुखं तेन मां नित्यं पाहि॥ 4.21
Oh one who is everywhere (कश्चित् भीरुः = both here no and there) the very notice/thought towards (प्रपद्यते) Him being the unborn (अजात इति एवम्) oh Rudra (हे रुद्र) your/that (यत् ते) auspicious right-hand side (दक्षिणम्) face (मुखम्) is/with which (तेन) you protect me/liberate me (माम् पाहि) ever/always (नित्यम्)

Svetasvatara Upaniṣhad 4.21

We covered Vedas and Upaniṣhad but what about the link to Itihāsa? Does it coincide with what we have explored above? An exact question was asked by Yudhishthria to Sri Krishna, so let’s see what was the reply:

Vāsudeva said, – O mighty armed Yudhishthria, listen to me as I recite thee the many names of Rudra as also the high blessedness of that high-souled one. The Rishi’s describe Mahādeva as Agni, and Sthānu, and Maheswara, as one eyed and three eyed, of universal form, and Śiva or the highly auspicious. Brāhmanas conversent with the Vedas say that the divine has two forms, again are subdivided into many forms. That form which is fierce and terrible is regarded as identical with Agni and lightening and Surya. That other form which is mind and auspicious with Righteousness and Water and Chandramas. The again, it is said that half his body is fire and half is Soma (or the moon). That form of his which is mild and auspicious is said to be engaged in the practice of the Brahmacharya vow. That other form of his which is supremely terrible is engaged in all operations of destruction in the universe. Because He is great (Mahat) and the Supreme lord of all (Ishvara), therefore is called Maheswara. And since he burns and oppresses, is keen and fierce, and endued with great energy and is engaged in eating flesh, and blood and marrow, He is said to be Rudra. Since He is the foremost of all the deities, and since His dominion and acquisition are very extensive, and since he protects the extensive universe (creation), therefore he is called Mahādeva. Since he is of the form or color of smoke, therefore he is called Dhurjjati. Since by all His acts He performs sacrifice for all and seeks the good (welbeing) of every creature, therefore he is called Śiva or the auspicious one.

Mahābhāratam Anuśāsanica Parva Section 161 (non-jaya section)

Vyasa said”, ‘Hearing these words of the lotus-born Brahma, Maheswara became gratified. Desirous of extending his grace, he laughed aloud. The celestials then gratified (with praise) both Uma and Rudra. The arm of the thunder-wielding Sakra re-got its natural state. That foremost one of all the gods, that destroyer of Daksha’s sacrifice, that divine lord having the bull for his sign, became gratified with the gods. He is Rudra he is Siva, he is Agni, he is everything, and he hath knowledge of everything. He is Indra, he is the Wind, he is the twin Aswins, and he is the lighting. He is Bhava, he is Parjanya, he is Mahadeva, he is sinless. He is the Moon, he is Isana, he is Surya, he is Varuna. He is Kala, he is Antaka, he is Mrityu, he is Yama. 1 He is the day, and he is the night. He is the fortnight, he is the month, he is the seasons. He is the morning and evening-twilights, he is the year. He is Dhatri, he is Vidhatri, he is the Soul of the universe, and he is the doer of all acts in the universe. Though himself without body, it is he who is the embodied celestial. 

Mahābhāratam Drona Parva Section 202-203 (jaya section)

Is this obvious enough? Unlike Rama or Kṛṣṇa, Śiva is not a given name. So, who is this Shankara who is Umapathi, and who has his abode in Kailash?

• One day a being walked in, whose name is not known ^{AB3.34, KA2.100sqq} as a Yogi, they said “He is Yoga and the Abode/Lord of Yoga”^DP203 so he became Adi Yogi, the first yogi who is one with creation.
• He is the one who brought forth the Seven Sages (saptarśi) as the Seven Gems^RV6.74.1.
• Since He had no name and came from the North (Mūjavant), and dwelled in mountains, they called him Girisha.
• As he was the foremost, they placed him on Dakshina and so called him Dakshina Murthi^SU4.21.
• Since he married the daughter of the mountain, as Kenopanishad says “Uma daughter of Himavat” they called him Umapathi ^{TA10.22.40.22/KU6} .
• All beings (bhootas) flocked around him, including pious, nefarious, and animals, especially snakes as they have unique chemistry with those in a meditative state, so they called him Paśūpati/Satpati/Bhootapati ^{TS4.5.2, RV2.33.12, AV11.2.1} so as an overlord of all beings they called him Isha. Those who were brave and courageous took a step towards him and so He became the leader of the brave ^RV10.92.9.
• He was independent and sovereign they called Svatantra, Svadhanva and Svatava ^RV1.166.2 (Sva = sovereign).
• Since he was the supreme overload/authority they called him Isha. So together he was titled Isha + Sva = Ishvar.
• In him they saw Mahat = the great principle, so they called him Maha + Isha + Svara = Mahesvara. In him they saw Vishvam, they called him Vishveswara. In him they saw everything (Sarva) so they called him Sarveshwara ^CKA2.100. They saw the highest Divinity in him so they called him Mahadeva ^SB6.3.
• They realized he was foremost and pure so they called him Sriṣṭhaḥ.
• They saw his janan:netra on his forehead so they called him Triambaka & Virupaksha.
• When he consumed the anti-creation element in his throat, they called him Nilakanta.
• He was fair to both devas and asuras so they called him Harikesha.
• He wore no clothes nor decorations so they called Digambara.
• He removed the darkness of Avidya so he was Andhashaspati.
• No one knows who he is, where he came from, they saw nothing but auspiciousness so they called Shiva.
• He removed their sufferings and gave them salvation so they called him Samkara.
• It’s childish to think a paper and a pen and a few words can describe what He is.

_{नमः शङ्क॒राय ^TS4.5.8 Samkara = Sam Karoti iti Samkara}

If we take Śrī Kṛṣṇa’s example in Gita, He is called with different names by Arjuna. Based on the situation and intimacy Arjuna called him Gudhakesha, Vasudeva, Yadava, Sakha, Hrishikesha, Janardana and many more, similarly various Rishi/Rśis like Vyāsa and Parashurama, Acharyas like Drona, and Krishna himself addressed this Nameless-Being-of-Bliss as Śiva (oh auspicious one), Shankara (the forgiver/remover of our troubles), Mahadeva (oh great one), Maheshwara (oh self supreme principle), Rudra (oh fierce one), Ishana/Ishava ^VS16.9 (the principle authority), and many more.

Many Upaniṣhads were later composed by Sages and Acharyas which are nothing but a summary of Vedas about Rudra. These later Upaniṣhads are considered Minor/Secondary because the primary Upaniṣhads do contain the cumulative essence of later Upaniṣhads. Hence Adi Śankaracharya was the first to collected Upaniṣhads belonging to various Vedic Śākhās along with Sutras to postulate the Advita theses. He foresaw the extinction of various Vedic Śākhās and hence preserved their Upaniṣhads. He on many occasions referred to minor Upaniṣhads like Jalabha Upaniṣhad in his Brahma Sutra Bhashya and more. It’s only after 1000 to 800 years later that other Acharyas influenced by the Puráńic literature relied on certain Upaniṣhads during the Bhakti era. So Śiva is the concept whereas Śankara is the personification of that concept. Śankara himself said to Maharśi Vaśiṣṭha:

Sankara said: Do you know who Divine is? Devine is not Viṣṇu, Sankara, or Brahmā; not the wind (Vāyu), the Sun or the Moon (Chandra/Soma); not the Brāhmans or the King; not I nor you; not Lakṣmī nor the mind (intellect). Divine is without form and undivided (not in the objects); that splendour (devanam) which is not made and which has neither beginning nor end is known as Deva or Śiva (the concept of eternal infinite auspiciousness) which is pure consciousness. That alone is to be worshipped; and that alone is all. If one is unable to worship this Śiva then he is encouraged to worship the form. The later yields finite results but the former bestows infinite bliss. He who ignores the infinite and is devoted to the finite abandons a pleasure-garden and seeks the thorny bush. However, sages sometimes worship a form playfully.

Rudra is the pure, spontaneous self-experience which is the one consciousness that dwells in all substances. It is the seed of all seeds, it is the essence of this world-appearance, it is the greatest of actions. It is the cause of all causes and it is the essence in all beings, though in fact it does not cause anything nor is it the concept of being, and therefore cannot be conceived. It is the awareness in all that is sentient, it knows itself as its own object, it is its own supreme object and it is aware of infinite diversity within itself.

Vaśiṣṭha Ramayanam / Yoga Vaśiṣṭham 6.1.29-30

At this time we should have experienced a glimpse into Śiva/Rudra as a divine concept that is beyond any object or form or a personified divinity. But let’s explore the evolution of Rudra and various concepts associated with Rudra.