In Tulasidas’s Shree Ramcharitmanas Lord Shiva tells Parvatiji that the Supreme Lord takes avatar and descends to earth for various reasons. One cannot pinpoint and say that the Lord takes avatar “only for this” reason.
सुनु गिरिजा हरिचरित सुहाए । बिपुल बिसद निगमागम गाए ।।
हरि अवतार हेतु जेहि होई । इदमित्थं कहि जाइ न सोई ।।
O Parvati! Listen, the Vedas and scriptures have sung the beautiful, detailed, and pure characters of Sri Hari. The reason for which Hari takes avatar cannot be said as ‘this is it’ because there can be many reasons which cannot be even comprehended by one’s material intellect.
The basic reason for Lord’s avatar is to establish dharma by defeating rakshas, spreading God’s glory, and giving bliss to the devotees. Lord Shiva then narrates different avatar stories of Lord Ram and Ravan in different kalpas. Here we are listing those stories.
Jay and Vijay become Ravan and Kumbhakarn
Once, Sanatkumaras went to Vaikuntha to get the darshan of Lord Vishnu. There they were stopped by two guards of Lord Vishnu known as Jay and Vijay. After a brief altercation, the four Kumaras cursed Jay and Vijay to fall from the Vaikuntha to be born as demons on Earth for 3 lifetimes. Same Jay-Vijay became Hiranyaksha Hiranyakashipu in one life and created havoc on Earth by their demonic deeds. Lord Vishnu took avatar as Varah and Narsimha to kill them and establish peace. They again took birth as Ravan and Kumbhakarn for the second time and were killed by Ram.
Once sage Narad sits for Tapasya in the Himalayas. As usual, Indra thinks that Narad is doing Tapasya to get his throne so he sends Kamdev to break the Tapasya. But such was Narad’s penance that Kamdev couldn’t break it. However, the defeat of Kamdev inflates Narad’s ego and he goes around Lord Shiva and Lord Vishnu boasting about it. To rescue Narad from the grip of ahankar (pride) Lord Vishnu creates a grandiose town whose king Sheelnidhi is organizing a Swayamvar of his beautiful daughter Vishwa Mohini. Narad loses his heart and mind on one glimpse of the princess. He wants to marry her but he is not confident in his own looks. So he goes to Lord Vishnu and asks for his help in giving him a beautiful face like that of Hari himself. Lord Vishnu instead of giving Narad a beautiful face gives him a monkey face. Unaware of the folly, Narad goes to the Swayamvar where he is mocked by all. Among them were two Shiv Ganas in disguise of Brahmans. They tease Narad the most and as a result, Narad curses them to be born as demons. Narad feels so bad because of the humiliation that he curses Lord Vishnu for separation from his beloved wife. To fulfill this curse Lord Vishnu takes the avatar as Lord Ram and the two Shiv Ganas become Ravan and Kumbhakarna.
In one Kalpa, the demon Jalandhar who was killed by Lord Shiva took rebirth as Ravan.
Once there was a virtuous King named Pratapbhanu. He with the help of his younger brother Ripumardan and the minister Dhramruchi defeated all his enemy kings and performed thousands of yajnas. One day while chasing a wild bore he comes into an association with a fake sage who in fact was one of Pratprudra’s enemies. The virtuous king doesn’t recognize the fake sage and gets so impressed by him that he agrees to a devious plan. The fake sage suggests that Pratapbhanu organize a feast for Brahmanas in his palace for a year. Doing so will satisfy the Brahmanas and Pratabhanu will be an undefeated king of the entire planet for thousands of years. The imposter with the help of a demon named Kalketu hatches a plot to trick the Brahmanas to eat impure food and make Pratpbhanu responsible for it so that he is cursed by them. The plot becomes successful. The Brahmans curse the good king Pratapbhanu to be born as demons with his entire family and ministers. The king thus becomes Ravan, his younger brother becomes Kumbhakarna and the minister Dhramaruchi becomes Vibhishan. Since they were innocent, Lord Ram takes avatar to rescue them from demonic life.
Manu and Satrupa (the first couple) did Tapasya. They wanted to have a darshan of the Supreme Lord in his Ram form. After many years of penance, Lord Ram along with mother Sita appeared in front of them and asked for a boon. On this Manu and Satrupa asked for a son “just like Lord Ram”. So, Lord Ram said since there is no one else in the universe just like him, he will take birth as Manu and Satrupa’s son and give them the honor and bliss of being the Supreme God’s parents. Same Manu and Satrupa took birth as king Dashrath and Kaushalya and Lord Ram took avatar as their son in the treta-yuga.
देखि प्रीति सुनि बचन अमोले । एवमस्तु करुनानिधि बोले ।।
आपु सरिस खोजौं कहँ जाई । नृप तव तनय होब मैं आई ।।
Seeing the king’s love and hearing his invaluable words, the Karunanidhan Bhagavan said – so be it. O, king! Where can I go to find [another] like myself? Therefore I myself will come and become your son.