According to Hindu mythology, Prithu is a sovereign named in the Vedic scriptures and considered an Avatar or incarnation of the preserver god Vishnu.
Prithu means abundance.
Mother Earth seeing the hard work of her children fulfilled all the desires of her children and gave them prosperity. The King was very pleased with her and he embraced and accepted her as his daughter. Thus she was also referred by the name Prithu, the daughter of Prithvi. So after this the king decided to conduct a yagna for the good of the people and the natural resources. The yagna was conducted on a major scale and the king invited all the devas of the celestial sphere and his people to the sacrifice. The sacrifice was also graced by Lord Vishnu. Lord Vishnu advised the king not to injure or neglect anyone and to treat all the living beings alike for it was he who lives in their soul. He also told the king not to be carried away either by joy or not to lose heart at time of difficulties for which the mind should be kept under total control and devoted to the Lord acting wise. Prithu prostrated before his Lord and accepted to follow his words and where he wished to have a mind which is always devoted to Sri Vishnu and sing and hear only the praises of Lord. After the sacrifice Sri Vishnu and the devas returned back to their respective places. Then Prithu began to teach all his subjects on how to gain supreme knowledge by doing rightly things in the world. He also taught them to dedicate and sincerely serve themselves to the Lord. By doing so apart from the mind becoming free from all impurities, they also learnt how to reach the lotus feet of Sri Vishnu by conquering death.
Narada thus to teach him a lesson came forward to tell Pracinbarhi a story. Once there lived a king who was not satisfied with what he had. So he went roaming about all over the world just looking for a place where all his desires could be satisfied. Finally after a long search he came across a beautiful place to the south of Himalayas and here he saw a huge palace with nine gates. Puranjana liked this place very much and thought this was the right place to live, so he decided to settle here. After this he met a beautiful looking lady in the palace to whom Purnajana was married to and soon became very much attached to her. He became so attached to her that he got into a state where if she cried he cried and if she wept, the king wept too. Thus soon the king totally lost his independence and became thoroughly dependent on her and lived like a slave to her. Since the king's pleasure was not constant but was transient he never felt satisfied even through the nine gates. Later his city was attacked and taken away and was totally ruined. Puranjana was thrown out and he also lost his wife. Thus the last few days of his life the king became mad knocking at the doors of others and finally died. Then the king was born as a beautiful young lady who got married to a king by name Malayadhvaja and they both loved each other very much. One day he found the king lying dead. She decided that she cannot live without her husband and so decided to burn herself in the funeral pyre of her husband. But then an old Brahmin came there and said to her to realize that she is neither a woman in this life who wanted to go along with her husband nor a man in the previous life that went behind a woman losing all his senses. The Brahmin said that "you are my own self - the one eternal reality. Shed your weakness. Awake to this truth."
Now Naradha elaborated clearly to Pracinabarhi that Puranjana in the story stands for Purusha, the self and the Brahmin was none other than the lord. The purusha who goes in search of a place where he can satisfy all his needs finally finds the human body which is the nine gates and starts enjoying the worldy pleasures including his wife. Identifying completely with this intellect or ego, he forgets his own divine nature and becomes full of ignorance and vanity. Finally he was thrown out by diseases and killed. Therefore once when man falls as a prey for fleeting pleasures of the world and forgets his divine nature, he gets more and more bounded to his intention or conscious deeds. The deed's which is done by the individuals intention to do decides a person's future birth.
Once in the next birth, the person realizes and regains his previous knowledge of that he is none other than the Eternal Brahman. Only after realizing the truth he becomes free of his karmas. Therefore, devote yourself to your own friend, for he is but you. Love him and be free. Only after hearing the story Pracinabarhi, the king who was confused of knowing what to do was clear and his mind was free from all impure thoughts he had about the worldly pleasures. Pracinabarhi not only loved the teachings of Naradha but also started to follow them very sincerely. Soon Pracinabarhi realized the teachings of Naradha about one's self and so he gave his kingdom to his sons and took off only to retire and realize the god in himself. So he went to Kapilashrama at the mouth of the Ganges to practice his way of truth or the teachings. Pracinabarhi was very true to the teachings and practiced it and soon became close to god and also one with him.