2 “Judge me, O Lord, and separate my cause from the ungodly nation”. I do not dread Your judgment, because I know Your mercy. “Judge me, O God,” he cries. Now, meanwhile, in this state of pilgrimage, Thou dost not yet separate my place, because I am to live together with the “tares” even to the time of the “harvest:” Thou dost not as yet separate my rain from theirs; my light from theirs: “separate my cause.” Let a difference be made between him who believes in You, and him who believes not in You. Our infirmity is the same; but our consciences not the same: our sufferings the same; but our longings not the same. “The desire of the ungodly shall perish,” but as to the desire of the righteous, we might well doubt, if He were not “sure” who promised. The object of our desires is He Himself, who promises: He will give us Himself, because He has already given Himself to us; He will give Himself in His immortality to us then immortal, even because He gave Himself in His mortality to us when mortal....
Source: The Enarrations, or Expositions, on the Psalms (New Advent)