dvitiyam tu bhavayasya
rasatala-gatam mahim
uddharisyann upadatta
yajnesah saukaram vapuh
SB 1.3.7

Translation
The supreme enjoyer of all sacrifices accepted the incarnation of a boar [the second incarnation], and for the welfare of the earth He lifted the earth from the nether regions of the universe.

Purport by Srila A.C. Bhaktivedanta Swami Prabhupada
The indication is that for each and every incarnation of the Personality of Godhead, the particular function executed is also mentioned. There cannot be any incarnation without a particular function, and such functions are always extraordinary. They are impossible for any living being to perform. The incarnation of the boar was to take the earth out of Pluto's region of filthy matter. Picking up something from a filthy place is done by a boar, and the all-powerful Personality of Godhead displayed this wonder to the asuras, who had hidden the earth in such a filthy place. There is nothing impossible for the Personality of Godhead, and although He played the part of a boar, by the devotees He is worshiped, staying always in transcendence.