Hymns sing to Rudras and Maruts as Earth-shaking clans feared by all lokas and are the only Divinities feared greatly by Rishis/Rśi. Since the Vedas revolve around Yajñá, the aspect of fear is seen in the discipline, devotion, and secrecy of the Yajamana and Adhvaryu towards their Dikṣhā (initiation and sanctity), meaning the one hosting the Yajñá and the one performing/chanting the mantras in the proper order (Ardhaka), else Rudra brings forth His wrath and consumes themTS1.6.7. Both sages and commoners feared the wrath of Rudras, but they knew that Rudras were not malicious. They understood the compassionate hand of the Rudras, hence they reached out to Rudras for protection, medicines, health, boons to bear children, boons to get a loving spouse, for wealth and prosperity VS3.57-59,RV6.74.1 like the hymn that says “Oh Rudra, harm us not, and abandon us not”RV7.46.5. But one has to ask, why Rudra? Why not Indra or Agni or Soma? Let’s see a few such examples of his fearful aspect of Rudra when it comes to Yajñá by traversing Atharva Veda to Yajur and finally to Rig Veda:
अस्त्रा नीलशिखण्डेन सहस्राक्षेण वाजिना । रुद्रेणार्धकघातिना तेन मा सम् अरामहि ॥11.2.7
Oh Rudra (रुद्र), with powerful/swift/impetuous (वाजिना ) mighty weapons (अस्त्र), with dark hair and chest (शिखण्ड) (or) Bluish-Black turf ((नील +शिख) , thousand eyes (सहस्राक्ष ) (or) dwelling in thousand places (सहस्र + क्षेण ), and inflictor/slayer (घातिन्) of Ardhaka (अर्धक), in this way (तेन ) one who alters (altering) and is improper (अराम ) chants the mantras (अर्धक)
Please note: Ardhaka (अर्धक) means improper utterance of Vedic mantras. शिखण्ड = Chest and शिख = Turf at the crown of the head. सहस्र + क्षेण = thousand places. सहस्राक्ष = thousand eyes. क्षयण = destruction and annihilation
यो अन्तरिक्षे तिष्ठति विष्टभितो ऽयज्वनः प्रमृणन् देवपीयून् । तस्मै नमो दशभिः शक्वरीभिः ॥11.2.23
The one who (यो ) dwells and establishes oneself firmly (तिष्ठति + विष्टभित) among the sky (अन्तरिक्षे ) destroys (प्रमृण) those who do not-sacrifice/insulting Divinities (अ-यज्वन् – देवपीयून् ) salutation and homage (नमो ) to the anger/fierce one (तस्मै ) we sign thy with ten (दशभिः ) hymns of Śākvara-Sāman (शक्वरीभिः )
अन्तरिक्षे = intermediator regions between Earth and Heavenly realms
भव राजन् यजमानाय मृड पशूनां हि पशुपतिर् बभूथ । यः श्रद्दधाति सन्ति देवा इति चतुष्पदे द्विपदे ऽस्य मृड ॥11.2.28Atharva Veda 11.2.7/23
Oh Bhava (भव ) you are the ruler/king (राजन् ) be gracious/favorable, pardon/spare (मृड ) towards the one hosting the Yagna (यजमानाय ) especially which donating cattle as sacrifice (पशूनां ) especially you are the one to reach (बभूथ ) being the lord of cattle (पशुपतिर् )| those who (यः ) have faith in the divine (श्रद्दधा श्रद्-दधान देवा ) view graciously (सन्ति) thus on (इति ) our four legged (चतुष्पदे ) and two legged (द्विपदे )
Please note: Yajamāna = the host of the ceremony, Adhvaryu = the one making oblations
Let’s visit one of the long-lost Vedic Śākhā, the Caraka-Katha Śākhā which gave forth Katha Upaniṣhad. Katha Śākhā has its own Saṃhitās, Brahmana, and Āraṇyaka which many like the German researcher Michael Witzel conclude to be earlier than the Tairtreya Śākhā of Kṛṣṇa Yajur. Like any Āraṇyaka, it primarily revolves around a particular aspect of Yajñá, so Katha Āraṇyaka too revolves around the concept of Pravargya which is a Soma ritual. As Michael Witzel says:
As an Aranyaka, it contains the secret doctrine of its particular Veda School (Sakha) and has to be studied in the wilderness (aranya). In the Katha Aranyaka, this is the Pravargya, a ritual in which a blazing clay vessel (mahavira) is identified with the Sun and Rudra Mahavira. This ritual also aims at giving the sponsor of the ritual (Yajamana) a new, heavenly body. This is established by multiple Upanishad-like identification between various entities of microcosm (man), ritual (Yajna), and macrocosm.
Please note: this heavenly body is a subtle body to ascend to heavens (sargo vai loka auttaravedikas III 233: 91.1-2)
An Aranyaka usually contains, as its nucleus, the most dangerous ritual held in highest esteem in a particular branch of the Veda. In the Rig Veda Aranyaka, it is the Mahavrata ceremony, the culmination of the one year gavam ayana Sattra ritual. In the Yajur Veda, however , it is the Pravargya ritual that is given this kind of special attention.
One of the foremost features of the Pravargya ritual is its dangerous appearance as a glowing vessel identified with the Sun and with Rudra Mahavira (II 89,II 100, III 207, 233, 238). The vessel is connected with Rudra, as it is baked by the sun (II 22, CF. II 89) udvāsana of the utensil takes place in the shape of the Sun (II151-54) further, the heated vessel is round like the Sun and glows like it. The red-hot vessel threatens all beings and even Heaven and Earth. Special protection is necessary for the priest (II 80sqq., II 180, 182-183), for the yajamāna (III 150, 173-76, etc.), for his wife (III 207, 177), even for the further offspring of the yajamāna (II 38, III 207), which otherwise would be born blind.
There also is a whole section on expiating (prayāŚcitti), aiming at the protection of the yajamāna from Rudra (III 235 sqq). The yajamāna retains long life when atoning for an accidental boiling over of the gharma vessel, or when atoning for thunder (sorrow), rain falling during the Pravargya ritual (hitting by a vajra), or setting of the Sun (back luck) while the Pravargay still is underway.
A priest (brahmana) who wants to spoil his own yajamāna for one reason or the another just has to alter one syllable…. Even the smallest mistake in ritual might lead to disaster: if certian mantras would be said loudly, Rudra would kill the yajamāna’s cattle (II 128A, cf. III 229).Caraka-Katha Aranyaka, Harvard Oriental Series 65, Michael Witzel
In the Katha Āraṇyaka‘s Pravargya ritual (Yajñá) the vessel (kalasha) used is called the Mahavira which is Identified with the brilliance of the Sun and Rudra as Rudra-Mahavira and so have to be performed very carefully after extended teachings and diksha (initiation and sanctity). Even during the Yagna any mistakes or mishaps have to be atoned else Rudra becomes the punisher, and can become Yama (death).
So, coming to our question, why Rudra? Because Rudra punishes Ardhaka (improper chanting) of Vedic Mantra and the sanctity of sacrifice of Yajñá and Divinities? Well the same Atharva Veda Chapter 11.2.17 in its very beginning answers this question and is well justified in Rig Veda 10.125.6
सहस्राक्षम् अतिपश्यं पुरस्ताद् रुद्रम् अस्यन्तं बहुधा विपश्चितम्।मोपाराम जिह्वयेयमानम् ॥AV 11.2.17Atharva Veda 11.2.17
Oh Rudra (रुद्र), thousand-eyed (सहस्राक्षम्) overseeing all /all-seeing through and through/directly (अति + पश्यसि + पुरस्तात्), at the end of our Yagna’s chanting Anuvākam (अस्य) Oh Multifold (बहुधा) wise (विपश्चित्) with prudent tough/divine speech ( जिह्व) gone after (येय) even and respectful ( मानम् )
Now, let’s evaluate Rudra’s divine speech aspect of Atharva Veda with Rig Veda.
अहं रुद्राय धनुरा तनोमि ब्रह्मद्विषे शरवे हन्तवा 10.125.6Rig Veda Mandala 10.125.6
I (अहं) (Vac the divine speech) (अहं) Rudra’s (रुद्राय) Bow (धनुरा) bend/stretch the bow string (तनोति) towards those who hostile to the sacred knowledge (ब्रह्म – द्विष्) swiftly (शर – वेग) to eliminate/kill (हन्तव्य)
Still, why Rudra? After reading the above we should pose more serious questions, we know Rudra punishes those who perform improper Yagna, and since Agni is the Hotr/the priest, and Agni is the Vedic Speech, Agni is the sacrificial fire, and Agni is the one who takes the Sacrifice of Yajna, then what does Rudra do with this sacrifice? Well, we might say Rudra is the Lord of that sacrifice and the lord of all Hymns, so Rudra receiving all the sacrifice of Yagna and all the Vedic mantras, but wait, isn’t Rudra the one who receives the remnant of the sacrifice? Yes, in many cases so that he can restart the Yagna treating the remnant as a whole. What about Soma, does He receive it and compete for Soma like Indra and others? No, Rudra is already conjoined with Soma. Then will Rudra distribute this sacrifice? Will Rudra decide what the Yajamana (Owner of Yajna) will receive? Well one might say, Rudra is Agni and Agni is Rudra and they both are the same, if so, then why does Agni become Rudra? Rather the correct question is, why does Rudra manifest in Agni? We asked a lot of serious questions so let’s see what Rig Veda and Yajur Veda has to say:
gātha-patim = Rudra the resort to all hymns/songs; medha-patim = Rudra the resort of Yajñá/Sacrifice/Oblations RV 1.43
Thou, Oh Agni, art Rudra, the Asura of the mighty sky, Rudra, lord of the sacrifice TS 1.3.14/1.4.11
कथा महे पुष्टिम्भराय पूष्णे कद्रुद्राय सुमखाय हविर्देKṛṣṇa Yajur Veda Taittirīya Saṃhitā 1.3.14, 1.4.11 / Rig Veda 1.43, 4.3.6-7
kathā́ mahé puṣṭimbharā́ya pūṣṇé b kád rudrā́ya súmakhāya havirdé
To the great Pushan () bestower of abundane, and to that Rudra (कद्रुद्राय = kád+Rudra), the high-sprited/energitic (सुमख) distributer of sacrifice (हविर्दे). RV4.3.7
कद्धिष्ण्यासु वृधसानो अग्ने कद्वाताय प्रतवसे शुभंये परिज्मने नासत्याय क्षे ब्रवः कदग्ने रुद्राय नृघ्ने RV 4.3.6
kád dhíṣṇyāsu vr̥dhasānó agne kád vātāya prátavase śubhaṁyé párijmane nā́satyāya kṣé brávaḥ kád agne rudrā́ya nr̥ghné
Oh Agni (अग्ने) we implore, blazing hight (वृधसान) from the dhíṣṇyā side of the Yajna alter, with powerful force (प्रतवस्) like wind (द्वात ) added to fire (कद्वाताय = kád+vātā +ya, ) lifing/raising up (शुभंया), encompassing the ground and surrounding the fire-alter/or Earth (परिज्मन् क्षे), what shall you (कदग्ने = kád+agne) say/tell to the dreadfull punisher (नृघ्ने) Rudra (of those who have perfomed improper Yagna/chant and who is the distributer of havis/sacrifice RV4.3.7).
Please note: कद्वाताय = adding stong wind, in this case its to fire. Similar to पश्चाद्वात = winds blowing to the west side.
Let’s visit Mahābhārata Itihāsam Section 285:
Thou art the beginning and thou art the end of the Vedas, thou art the Gāyatri and thou art OM. Thou art the fire upon which the sacrificial butter/ghee is poured. Thou art he who pours the ghee. Thou art he in honor of whom the ghee is poured, thou art the butter itself that is poured. Thou art those section of Brahmanas that are called Trisuparna, thou art all the Vedas, thou art the section called Śatarudrīya in the Yajushes/Yajur. Thou art holiest of holies, auspicious of auspicious things. Thou animates the inanimate body. Thou art the Chit that dwell in the human form.Mahābhāratam Moksha Dharma Parva Section 285
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)
Sri Krishna says to Yudhishthira about Rudra: Brāhmanas conversant with the Vedas says that the divine has two forms. One of these is terrible, and the other mild and auspicious. Those two forms, again, are subdivided into many forms3. That form which is fierce and terrible is regarded as identical with Agni, and Lightening (Asani), and Surya. That other from which is mild and auspicious is identical with Righteousness and Water and Chandramas4. Then again, it is said that half of his body is fire and half is Soma (or the moon).Mahābhāratam Anuśāsanica Parva Section 161 (non-jaya section)