2 But this being the case, how to this opinion that should not be contrary which the Apostle says, “For we shall all stand before the judgment-seat of Christ, that each may receive according to the things he has done by the body, whether good or bad;” this, you signify, you do not well see. For this apostolic sentence does before death admonish to be done, that which may profit after death; not then, first, when there is to be now a receiving of that which a person shall have done before death.
True, but this question is thus solved, namely, that there is a certain kind of life by which is acquired, while one lives in this body, that it should be possible for these things to be of some help to the departed; and, consequently, it is “according to the things done by the body,” that they are aided by the things which shall, after they have left the body, be religiously done on their behalf. For there are whom these things aid nothing at all, namely, when they are done either for persons whose merits are so evil, that neither by such things are they worthy to be aided; or for persons whose merits are so good, that of such things they have no need as aids.
Of the kind of life, therefore, which each has led by the body, does it come, that these things profit or profit not, whatever are piously done on his behalf when he has left the body. For touching merit whereby these things profit, if none have been gotten in this life, it is in vain sought after this life. So it comes to pass as well that not unmeaningly does the Church, or care of friends, bestow upon the departed whatever of religion it shall be able; as also that, nevertheless, each receives “according to the things which he has done by the body, whether it be good or bad,” the Lord rendering unto each according to his works. For, that this which is bestowed should be capable of profiting him after the body, this was acquired in that life which he has led in the body.
Source: On Care to be Had For the Dead (New Advent)