Augustine of Hippo

There are two ways to interpret the affirmation that he "shall judge the living and the dead." On the one hand, we may understand by "the living" those who are not yet dead but who will be found living in the flesh when he comes; and we may understand by "the dead" those who have left the body or who shall have left it before his coming. Or, on the other hand, "the living" may signify "the righteous," and "the dead" may signify "the unrighteous"—since the righteous are to be judged as well as the unrighteous. For sometimes the judgment of God is passed on the evil people, as in the word, "But they who have done evil [shall come forth] to the resurrection of judgment." And sometimes it is passed on the good, as in the word, "Save me, O God, by your name, and judge me in your strength." Indeed, it is by the judgment of God that the distinction between good and evil is made, to the end that, being freed from evil and not destroyed with the evildoers, the good may be set apart at his right hand. This is why the psalmist cried, "Judge me, O God," and, as if to explain what he had said, "and defend my cause against an unholy nation."