In this sacrament, the sinner, placing himself before the merciful judgment of God, anticipates in a certain way the judgment to which he will be subjected at the end of his earthly life. For it is now, in this life, that we are offered the choice between life and death, and it is only by the road of conversion that we can enter the Kingdom, from which one is excluded by grave sin. In converting to Christ through penance and faith, the sinner passes from death to life and "does not come into judgment."
Source: Catechism of the Catholic Church (Vatican.va)