Christ will not be the only one to judge on that day; others will be associated with Him. Of these, some will judge only in the sense of serving as a basis for comparison. In this way the good will judge the less good, or the wicked will judge the more wicked, according to Matthew 12:41: “The men of Nineveh shall rise in judgment with this generation and shall condemn it.” And some will judge by giving their approval to ‘the sentence; in this way all the just shall judge, according to Wisdom 3:7 ff: “The just… shall judge nations.” But some will judge with a certain judicial power delegated to them by Christ, having “two-edged swords in their hands,” as is indicated in Psalm 149:6.
This last kind of judicial power the Lord promised to the apostles, in Matthew 19:28, when He said: “You who have followed Me, in the regeneration, when the Son of man shall sit on the seat of His majesty you also shall sit on twelve seats, judging the twelve tribes of Israel.” We are not to conclude from this that only the Jews who belong to the twelve tribes of Israel will be judged by the apostles, for by the twelve tribes of Israel are understood all the faithful who have been admitted to the faith of the patriarchs. As for infidels, they will not be judged, but have already been judged.
Similarly, the twelve apostles who walked with Christ during His earthly life are not the only ones who will judge. Judas assuredly will not judge, and Paul, on the other hand, who labored more than the rest, will not lack judicial power, especially as he himself says, 1 Corinthians 6:3: “Know you not that we shall judge angels?” This dignity pertains properly to those who have left all to follow Christ, for such was the promise made to Peter in answer to his question in Matthew 19:27: “Behold, we have left all things and have followed Thee; what therefore shall we have?” The same thought occurs in Job 36:6: “He gives judgment to the poor.”
And this is reasonable, because, as we said, the investigation will deal with the actions of men who have used earthly things well or ill. Correctness of judgment requires that the mind of the judge should be unswayed by those matters about which he has to judge; and so the fact that some have their minds completely detached from earthly things gives them a title to judicial authority.
The announcing of the divine commandments also contributes to the meriting of this dignity. In Matthew 25:31 we read that Christ will come to judge accompanied by angels, that is, by preachers, as Augustine suggests in a work on penance [Sermo 351, De utilitate agendae poenitentiae]. For they who have made known the precepts of life ought to have a part in examining the actions of men regarding the observance of the divine precepts.
The persons mentioned will judge by cooperating in the task of revealing to each individual the cause of the salvation or damnation both of himself and of others, in the way that higher angels are said to illuminate the lower angels and also men.
We profess that this judicial power belongs to Christ when we say, in the Apostles’ Creed: “From thence He shall come to judge the living and the dead.”
St. Thomas Aquinas. (1265-1274). Compendium Theologiae: Role of the Saints in the Judgment, trans. by Cyril Vollert. St. Louis & London: B. Herder Book Co., 1947
All scripture is given by inspiration of God and is profitable for doctrine, reproof, correction, and instruction in righteousness (2 Timothy 3:16).