Why was Rudrani born as Devi Sati and Parvati?

Question

I’m assuming Rudrani=Sati/Parvati for the purposes of the question.

Lord Rudra emerges from the forehead of Brahmaji and takes on 11 names and places (Ekadasha Rudra). Here Brahmaji also gives these 11 forms wives:

धीर्धृतिरसलोमा च नियुत्सर्पिरिलाम्बिका । इरावती स्वधा दीक्षा रुद्राण्यो रुद्र ते स्त्रिय:॥१३॥

O Rudra, you also have eleven wives, called the Rudrāṇīs, and they are as follows: Dhī, Dhṛti, Rasalā, Umā, Niyut, Sarpi, Ilā, Ambikā, Irāvatī, Svadhā and Dīkṣā.

-Śrimad Bhāgavatam 3.12.13

There is also something called a Rudrasrshti (the Bhairavas and other such forms) which happens thereafter, which is possible only between male and female (both Rudra and Rudrani).

This means that Lord Shiva was married to Rudrani from the time of his emergence from Brahmaji which is a very long time ago.

Question

Why then did Rudrani need to take birth as Dakshayani to remarry Lord Shiva? Why did she need to leave him in the first place?

Also why could Sati not have reverted to her Rudrani form and married Lord shiva again. What was the necessity for Parvati birth?

Or was it the case that Lord Shiva was a bachelor right until Daksha begot progeny? Who then is this Rudrani, the supposed wife of Rudra?

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^{As far as I remember as per Devi Purana Daksha had prayed to shakti to be born as his daughter. It is not a very convincing reason for her to completely leave Shiva’s side. She could’ve been born as well as remained with shiva. I would like a more convincing story.}

Answer 1

You see the biggest confusion occurs when you think Kālāgni Rudra = Ekadasha Rudra. Which is a misconception. As Kailash Pati Rudra ≠ 11 Rudras.

Yes, they have same names even their consorts names are also mostly same.

This chapter of Shiva Purana explains how Lord Brahma was unable to create females so the creation could not going ahead so he prayed to Lord Shiva/ā (Ardhanarishwara) and due to their boon Maa Uma got seperated from Bhagawan Shiva to create females. And Lord Brahma also prayed to her to born as his granddaughter to marry Kailash Pati Rudra (Who was born of Bhagawān Shiva's heart).

The 11 Rudras in different kalpas take birth from different people.

Sometimes from Lord Brahma.:

Linga Purana 1.22.:

23. From the body of Brahmā of unequalled valour, the eleven Rudras sprang up crying, out of sympathy and mercy.

24. They became known as Rudras due to their crying. The Rudras and the prāṇas are identical with each other.

MBH.:

“Then sprang Rudra from the principle of wrath, starting into life, Rudra created ten others that were like him. These eleven Rudras are called by name of Vikara-Purushas”. (MBH 12:349:36).

Sometimes from Mata Surabhi.:

Shiva Purana 3.18.:

24. Then, in order to keep his promise Śiva was born of Surabhi assuming eleven forms.

Mahabharata HV Parva.:

“The ancient histories confirm that, the amR^ita (nectar), the brAhmaNas, the cows and rudras are the children of surabhi. These are the children of kashyapa”. (Harivamsa Parva 3:36:50-51).

“Hallowed by her own ascesis and by the grace of mahadeva, the daughter of daskha prajApati, and the wife of kashyapa prajApati, lady surabhi, moulded eleven rudrA-s”. (Harivamsa Parva 1:3:49-50 ).

Sometimes from Mata Aditi.:

Valmiki Ramayana.:

“Aditi gave birth to twelve Aditya-s, the Sun-gods, eight Vasu-s, the Terrestrials-gods, eleven Rudraa-s, the Fury-gods, and two Ashvinis, the medicine-gods, total thirty-three of them”. (Valmiki Ramayana 3-14-14).

Sometimes from SeshNaag.:

Srimad Devi Bhagwatam 8.20.:

1-37. . . . When he wants to destroy all this during the Pralaya, the very powerful Sankarṣaṇa (Sesa) Rudra, well arrayed with the eleven Vyūhas, military (squadrons) arrangements, springs up from Him. From His Central Eyebrow, looking wide with His Three Eyes and raising His Trident, resplendent with three flames. . .

and so on.

The 11 Rudras are the minor expansions of Bhagawān Shiva with same look weapons wifes, etc same as among 12 Aditya, Vishnu is there.

Mahabharata clearly distinguishes them as follows.:

MBH.:

“Vaisampayana said, 'It is known that the spiritual sons of Brahman were the six great Rishis (already mentioned). There was another of the name of Sthanu. And the eleven sons of Sthanu, gifted with great energy, were, it is known, eleven. They were Mrigavayadha, Sarpa, Niriti of great fame: Ajaikapat, Ahivradhna, and Pinaki, the oppressor of foes; Dahana and Iswara, and Kapali of great splendour; and Sthanu, and the illustrious Bharga. These are called the eleven Rudras”. (MBH 1:67:1–3).

As you can see even one of the sons is also called as Sthanu. Let's see another example which will make it crystal clear.

“"Daksha said, 'We have many Rudras armed with lances and bearing matted locks on their heads. They are eleven in number. I know them all, but I do not know who this (new Rudra) Maheswara is.'”. (MBH 12:290:20).

I hope this clarifies your queries.