Christ is Lord of eternal life. Full right to pass definitive judgement on the works and hearts of men belongs to him as redeemer of the world. He "acquired" this right by his cross. The Father has given "all judgement to the Son". Yet the Son did not come to judge, but to save and to give the life he has in himself. By rejecting grace in this life, one already judges oneself, receives according to one's works, and can even condemn oneself for all eternity by rejecting the Spirit of love.
Source: Catechism of the Catholic Church (Vatican.va)