III. Penitence is sure only in this life.
But if any one of those for whom we entreat God be hindered by some obstacle and lose the benefit of immediate absolution, and before he attain to the remedies appointed, end his days in the course of nature, he will not be able when stripped of the flesh to gain that which when yet in the body he did not receive. And there will be no need for us to weigh the merits and acts of those who have thus died, seeing that the Lord our God, whose judgments cannot be found out, has reserved for His own decision that which our priestly ministry could not complete: for He wishes His power to be so feared that this fear may benefit all, and every one may dread that which happens to the lukewarm or careless. For it is most expedient and essential that the guilt of sins should be loosed by priestly supplication before the last day of life.
Source: Letters (New Advent)