10 But I see what is next required of us; in like manner as in the case of the five virgins, a reason was given why many should belong to five, and why to those five many Jews, and why to a hundred and fifty-three many perfect— to show why and how to the twelve thrones not twelve men, but many belong. What mean the twelve thrones, which signify all men everywhere that have been enabled to be so perfect as they must be perfect, to whom it is said, “You shall sit over the twelve tribes of Israel”? And why do all men everywhere belong to the number twelve?
Because the very “everywhere” which we say, we say of the whole world: but the compass of lands is contained in four particular quarters, East, West, South, and North: from all these quarters they being called in the Trinity and made perfect in the faith and precept of the Trinity,— seeing that three times four are twelve, you perceive wherefore the saints belong to the whole world; they that shall sit upon twelve thrones to judge the twelve tribes of Israel, since the twelve tribes of Israel, also, are the twelve tribes of the whole of Israel.
For like as they that are to judge are from the whole world, so also they that are to be judged are from the whole world. The Apostle Paul of himself, when he was reproving believing laymen, because they referred not their causes to the Church, but dragged them with whom they had matters before the public, said, “Do you not know that we shall judge Angels?” See after what sort He has made Himself judge: not only himself, but also all that judge aright in the Church.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)