Rig veda (Nasadiya Suktam) 10:129:4 says :
" kāmas tad agre sam avartatādhi manaso retah prathamam yad āsit"
ie., Kâma rose in the beginning, Kâma, the primal seed and germ of Spirit.
The Whole creation aroused because of union of Shiva and Shakti.
Rudra's form is very terrifying. Even the vedik Rishis feared to utter the very name "Rudra". Instead of this name, the Rishis preferred to call him " This God" , "That God" or with other names like "Agni", "pashupati","Manyu","ugrá "..etc. Because of the terror of Rudra, fire burns,because of the terror of Rudra, the sun shines, Because of the terror of Rudra, The gods like Indra and Vayu and Death, the fifth,run.(bhayād asyāgnis tapati, bhayāt tapati sῡryaḥ: bhayād indraś ca vayuś ca, mṛtyur dhavati pañcamaḥ.) . Rudra is truly Nirguna Nirakara parabrahman, But,for the sake of administrating the worlds he takes different forms . some forms are terrifying while others are auspicious. When a hymn is addressed to Rudra, the singer begs for auspicious forms only and avoids terrifying forms. Even in Satarudriyam of Yajurveda , we can see the seer asking Rudra to appear before him in his Shiva form.
Yaa te rudra shiva tanu raghoraapapakashini
Taya nastanuva shantamaya girishantabhichakashihi ( Yajurveda iv:5:1c)
That body of thine, O Rudra, which is kindly,Not dread, with auspicious look,With that body, most potent to heal,O haunter of the mountains, do thou look on us.
Similarly, Here ( Atharva Veda 9:2:25) also , Lord Rudra(Kâma) is asked leave his ugrá form and appear in glorious śivā́ form.
sapatnahánam r̥ṣabháṃ ghr̥téna kā́maṃ śikṣāmi havíṣā́jyena
nīcáiḥ sapátnān máma padaya tvám abhíṣṭuto mahatā́ vīryèṇa 1
To the bull that slays the enemy, to Kâma, do I render tribute with ghee, oblation, and (sacrificial) melted butter. Do thou, since thou hast been extolled, hurl down my enemies by thy great might!
yán me mánaso ná priyáṃ cákṣuṣo yán me bábhasti nā́bhinándati
tád duṣvápnyaṃ práti muñcāmi sapátne kā́maṃ stutvód aháṃ bhideyam 2
The evil dream which is offensive to my mind and eye, which harasses and does not please me, that (dream) do I let loose upon my enemy. Having praised Kâma may I prevail!
duṣvápnyaṃ kāma duritáṃ ca kamāprajástām asvagátām ávartim
ugrá ī́śānaḥ práti muñca tásmin yó asmábhyam aṃhūraṇā́ cíkitsāt 3
Evil dreams, O Kâma, and misfortune, O Kâma, childlessness, ill-health, and trouble, do thou O ugrá O ī́śānaḥ , let loose upon him that designs evil against us!
nudásva kāma prá ṇudasva kāmā́vartiṃ yantu máma yé sapátnāḥ
téṣāṃ nuttā́nām adhamā́ támāṃsy ágne vā́stūni nír daha tvám 4
Drive them away, O Kâma, thrust them away, O Kâma; may they that are my enemies fall into trouble! When they have been driven into the nethermost darkness, do thou, O Agni, burn up their d welling- places!
sā́ te kāma duhitā́ dhenúr ucyate yā́m āhúr vā́caṃ kaváyo virā́jam
táyā sapátnān pári vr̥ṅgdhi yé máma páry enān prāṇáḥ paśávo jī́vanaṃ vr̥ṇaktu 5
That milch-cow, O Kâma, whom the sages call Vâk Virâg (ruling, or resplendent speech), is said to be thy daughter; by her drive away my enemies; breath, cattle, and life shall give them a wide birth!
kā́masyéndrasya váruṇasya rā́jño víṣṇor bálena savitúḥ savéna
agnér hotréṇa prá ṇude sapátnāṃ chambī́va nā́vam udakéṣu dhī́raḥ 6
With the strength of Kâma, Indra, king Varuna, and Vishnu, with the impelling force (savena) of Savitar, with the priestly power of Agni, do I drive forth the enemies, as a skilled steersman a boat.
ádhyakṣo vājī́ máma kā́ma ugráḥ kr̥ṇótu máhyam asapatnám evá
víśve devā́ máma nātháṃ bhavantu sárve devā́ hávam ā́ yantu ma imám 7
My sturdy guardian, ugráḥ Kâma, shall procure for me full freedom from enmity! May the gods collectively be my refuge, may all the gods respond to this, my invocation!
idám ā́jyaṃ ghr̥távaj juṣāṇā́ḥ kā́majyeṣṭhā ihá mādayadhvam
kr̥ṇvánto máhyam asapatnám evá 8
Taking pleasure in this (sacrificial) melted butter, and ghee do ye, (O gods), of whom Kâma is the highest, be joyful in this place, procuring for me full freedom from enmity
indrāgnī́ kāma saráthaṃ hí bhūtvā́ nīcáiḥ sapátnān máma pādayāthaḥ
téṣāṃ pannā́nām adhamā́ támāṃsy ágne vā́stūny anunírdaha tvám 9
O Indra and Agni, and Kâma, having formed an alliance, do ye hurl down my enemies; when they have fallen into the nethermost darkness, do thou, O Agni, burn up after them their dwelling places!
jahí tvám kāma máma yé sapátnā andhā́ támāṃsy áva pādayainān
nírindriyā arasā́ḥ santu sárve mā́ té jīviṣuḥ katamác canā́haḥ 10
Slay thou, O Kâma, those that are my enemies, hurl them down into blind darkness. Devoid of vigour, Without sap let them all be; they shall not live a single day!
ávadhīt kā́mo máma yé sapátnā urúṃ lokám akaran máhyam edhatúm
máhyaṃ namantāṃ pradíśaś cátasro máhyaṃ ṣáḍ urvī́r ghr̥tám ā́ vahantu 11
Kâma has slain those that are my enemies, a broad space has he furnished me to thrive in. May the four directions of space bow down to me, and the six broad (regions) carry ghee to me!
té 'dharā́ñcaḥ prá plavantāṃ chinnā́ náur iva bándhanāt
ná sā́yakapraṇuttānāṃ púnar asti nivártanam 12
They (the enemies) shall float down like a boat cut loose from its moorings! There is no returning again for those who have been struck by our missiles.
agnír yáva índro yávaḥ sómo yávaḥ
yavayā́vāno devā́ yavayantv enam 13
Agni is a defence, Indra a defence, Soma a defence. May the gods, who by their defence ward off (the enemy), ward him off!
ásarvavīraś caratu práṇutto dvéṣyo mitrā́nāṃ parivargyàḥ svā́nām
utá pr̥thivyā́m áva syanti vidyúta ugró vo deváḥ prá mr̥ṇat sapátnān 14
With his men reduced, driven out, the hated (enemy) shall go, shunned by his own friends! And down upon the earth do the lightnings alight; may that god ugra crush your enemies!
cyutā́ ceyáṃ br̥haty ácyutā ca vidyúd bibharti stanayitnū́ṃś ca sárvān
udyánn ādityó dráviṇena téjasā nīcáiḥ sapátnān nudatāṃ me sáhasvān 15
This mighty lightning supports both moveable(falliable) and immoveable(infalliable) things, as well as all thunders. May the risingsun by his resources and his majesty hurl down my enemies, lie the mighty one!
yát te kāma śárma trivárūtham udbhú bráhma várma vítatam anativyādhyàṃ kr̥tám
téna sapátnān pári vr̥ṅgdhi yé máma páry enān prāṇáḥ paśávo jī́vanaṃ vr̥ṇaktu 16
With that triple-armoured powerful covering of thine, O Kâma, with the charm that has been made into an Invulnerate armour spread (over thee), with that do thou drive away those who are my enemies; may breath, cattle, and life give them a wide berth!
yéna devā́ ásurān prā́ṇudanta yénéndro dásyūn adhamáṃ támo ninā́ya
téna tváṃ kāma máma yé sapátnās tā́n asmā́l lokā́t prá ṇudasva dūrám 17
With the weapon with which the god drove forth the Asuras, with which Indra led the Dasyus to the nethermost darkness, with that do thou, O Kâma, drive forth far away from this world those who are my enemies!
yáthā devā́ ásurān prā́ṇudanta yáthéndro dásyūn adhamáṃ támo babādhé
táthā tváṃ kāma máma yé sapátnās tā́n asmā́l lokā́t prá ṇudasva dūrám 18
As the gods drove forth the Asuras, as Indra. forced the demons into the nethermost darkness, thus do thou, O Kâma, drive forth far away from this world those who are my enemies!
kā́mo jajñe prathamó náinaṃ devā́ āpuḥ pitáro ná mártyāḥ
tátas tvám asi jyā́yān viśváhā mahā́ṃs tásmai te kāma náma ít kr̥nomi 19
Kâma was born at first; him neither the gods, nor the Fathers, nor men have equalled. To these art thou superior, and ever great; to thee, O Kâma, do I verily offer reverence.
yā́vatī dyā́vāpr̥thivī́ varimṇā́ yā́vad ā́paḥ siṣyadúr yā́vad agníḥ
tátas tvám asi jyā́yān viśváhā mahā́ṃs tásmai te kāma náma ít kr̥ṇomi 20
O Kâma, You are greater than all. You are higher than Heaven and wider than the Earth. You are farther than the waters have swept and hotter than fire. To that Kâma, do I verily offer reverence.
yā́vatīr díśaḥ pradíśo víṣūcīr yā́vatīr ā́śā abhicákṣaṇā diváḥ
tátas tvám asi jyā́yān viśváhā mahā́ṃs tásmai te kāma náma ít kr̥ṇomi 21
Great as are the directions (of space) and the intermediate direction on either side, great as are the regions and the vistas of the sky; to these art thou superior, To that Kâma, do I verily offer reverence
yā́vatīr bhŕ̥ṅgā jatvàḥ kurū́ravo yā́vatīr vághā vr̥kṣasarpyò babhūvúḥ
tátas tvám asi jyā́yān viśváhā mahā́ṃs tásmai te kāma náma ít kr̥ṇomi 22
As many bees, bats, kurûru-worms, as many vaghas and tree-serpents as there are; to these art thou superior . To that Kâma, do I verily offer reverence
jyā́yān nimiṣató 'si tíṣṭhato jyā́yānt samudrā́d asi kāma manyo
tátas tvám asi jyā́yān viśváhā mahā́ṃs tásmai te kāma náma ít kr̥nomi 23
Superior art thou to all that winks (lives), superior to all that stands still (is not alive), superior to the ocean art thou, O Kâma Manyu! To these art thou superior . To that Kâma, do I verily offer reverence
ná vái vā́taś caná kā́mam āpnoti nā́gníḥ sū́ryo nótá candrámāḥ
tátas tvám asi jyā́yān viśváhā mahā́ṃs tásmai te kāma náma ít kr̥ṇomi 24
O Kama, You are greater than all. You are faster than the wind, hotter than the Sun and greater than the Moon. You are farther than the waters have swept and hotter than fire. O Love, You are greater than all.Kâma, do I verily offer reverence
yā́s te śivā́s tanvàḥ kāma bhadrā́ yā́bhiḥ satyáṃ bhávati yád vr̥ṇiṣé
tā́bhiṣ ṭvám asmā́m̐ abhisáṃviśasvānyátra pāpī́r ápa veśayā dhíyaḥ 25
With those auspicious(śivā́h) and gracious forms of thine, O Kâma, through which what thou wilst becometh reaL with these do thou enter into us, and elsewhere send the evil thoughts!