Other source:

Mr. Popo finally agrees to train Goku after seeing his potential. At the same time, Tienshinhan vows to train hard to beat Goku in the next Martial Arts Tournament. Realizing Goku’s determination, Kami reveals himself to Goku, who is shocked by his appearance and the story he tells. Kami agrees to revive the Eternal Dragon if Goku will stay and train with Mr. Popo for a while, terms which Goku gladly accepts.