PURPORT

Lord Visnu, who lies in the ocean of milk, incarnates Himself in various forms to maintain the laws of the cosmos and annihilate the causes of disturbance. Such incarnations are visible in every manvantara (i.e., in the course of the reign of each Manu, who lives for 71 x 4,300,000 years). Fourteen such Manus take their birth and die, to yield a place for the next, during one day of Brahma.