Why "Revantha" the youngest son of Sun god went to Vishnu's abode?
The story is told in this chapter and subsequent chapters of the Devi Bhagavatam. Surya's son Revanta, king of the Guhyakas, goes to Vaikuntha in order to see Vishnu. He comes riding on Ucchaishravas, a horse that came out of the churning of the ocean. Because Lakshmi was also born from the churning of the ocean, Ucchaishravas is her brother, so she keeps staring at it, to the point of ignoring Vishnu. So Vishnu puts a curse on her that she will live on Earth as a horse:
O Beautiful-eyed One! What you are looking at so intently? Are you so much enchanted with the sight of the horse that you are not speaking to me a single word, though I am repeatedly asking you so often! You lovingly dwell on all the objects; hence your name is Ramâ; your mind is also very restless, therefore you would be known as Chanchalâ Devî (the restless Devî). O Auspicious One! You are restless like ordinary women; you can never stay steadily for a certain time at any one place. While sitting before Me, you are enchanted with the sight of a horse; then you be born as a mare in that world of men, full of dreadful troubles, on the surface of the earth.
So Lakshmi descends to the Earth as a horse, and starts engaging in Tapasya in order to be reunited with Vishnu. Finally Vishnu comes there, also in the form of a horse, and in horse-form Vishnu and Lakshmi have a child named Ekavira, AKA Haihaya. Vishnu and Lakshmi go back to Vaikuntha, but Ekavira is adopted by Yayati's son Turvasu. Ekavira eventually becomes king himself, and because his other name is Haihaya his race become known as the Haihayas. Here is a description of Ekavira's descendants:
Then, in course of time, in the womb of Ekâvalî the King Haihaya got a son named Kritavîrya. The son of this Kritavîrya is known as Kârtavîrya. O King! Thus I have narrated to you the origin of the Haihaya dynasty.
The son of Kritavirya, Kartavirya Arjuna, was the famous king killed by Vishnu's incarnation Parashurama. And Kartavirya Arjuna is said to have been an incarnation of Vishnu's Sudarshana Chakra.
One note of caution: the Devi Bhagavatam is considered to have a lot of interpolations, and as far as I know this story isn't found in any of the Mahapuranas; in other Puranas the Haihayas are said to have been descended from another son of Yayati. So take this story with a grain of salt.
I have got a little confusion here. Is Ekavira a horse or human. He seems to be human as he becomes king and has his lineage going forward but confused about how come he is not a horse when both Lord Vishnu and Goddess Lakshmi were in horse form.– AbySep 9, 2015 at 14:25
1@Aby Ekavira was a human. I guess Vishnu and Lakshmi could make their child into anything they wanted, so they chose to make it human. By the way, Surya and Sanjana also had three children in horse form, namely the two Ashwini Kumaras and Revanta; see my answer here: hinduism.stackexchange.com/a/545/36 They weren't horses either. Sep 9, 2015 at 14:33
@Keshav - Which scripture says that Karttaveerya Arjuna is considered as Sudharshana amsa?– user808Sep 10, 2015 at 12:14
@Krishna it's mentioned in the Brahmanda Purana, and in this excerpt from the Narada Purana: i.imgur.com/Nf8w0Qi.jpg "He was the incarnation of Sudarshana Chakra on the earth." It's actually really funny, there are two chapters in the Narada Purana full of mantras to Kartavirya Arjuna, including a Kartavirya Gayatri mantra, a Kartavirya Kavacham, and a list of 108 names of Kartavirya Arjuna. It's funny that that the villain of the Parashurama story is also worshipped. Sep 10, 2015 at 12:32
@Krishna By the way, the story I've always heard is that the Sudarshana once got too arrogant, and told Vishnu that he was only able to defeat all these demons because of the Sudarsshana Chakra's help. So Vishnu cursed Sudarshana to be born on Earth, and told him that he would be born as Parashurama and kill him without using the Sudarshana Chakra, even though Sudarshana would have his thousand arms. I'm not sure whether it's mentioned in Hindu scripture though. I may post a question about that. Sep 10, 2015 at 12:36