After a thousand years of Churning of the Milky Ocean Dhanvantari arose with a water-pot (kamandalu) in one hand and a staff (danda) in the other. He rose above the water and worshipped Vishnu. He delivered the amrita, the drink of immortality, which was supposed to be shared equally by devas and asuras (demons). Vishnu promised him a wonderful rebirth.
So Dhanvantari was reborn to introduce the science of Ayurveda (the indigenous medicine of India), after his earthly father-to-be, Dhanva, worshipped his son-to-be as Abja-deva, the name Vishnu had given Dhanvantari as his divine name. Dhanvantari taught his disciples the Ayurveda.