12 And again, from the thought of those joys he returns to his own sighs. He sees what has come before in hope, and where he is in reality....Therefore returning to the groans proper to this place, he says, “O Lord God of virtues, hear my prayer: hearken, O God of Jacob”: for Jacob himself also You have made Israel out of Jacob. For God appeared unto him, and he was called Israel, seeing God. Hear me therefore, O God of Jacob, and make me Israel. When shall I become Israel? When the God of Gods shall appear in Sion.
13. “Behold, O God our defender. And look on the face of Your Christ”. For when does God not look upon the face of His Christ? What is this, “Look on the face of Your Christ”? By the face we are known. What is it then, Look on the face of Your Christ? Cause Your Christ to become known to all. Look on the face of Your Christ: let Christ become known to all, that we may be able to go from strength to strength, that grace may abound, since sin has abounded.
14. “For one day in Your courts is better than a thousand”. Those courts they were for which he sighed, for which he fainted. “My soul longs and fails for the courts of the Lord:” one day there is better than a thousand days. Men long for thousands of days, and wish to live here long: let them despise these thousands of days, let them long for one day, which has neither rising nor setting: one day, an everlasting day, to which no yesterday yields, which no tomorrow presses. Let this one day be longed for by us. What have we to do with a thousand days? We go from the thousand days to one day; let us hasten to that one day, as we go from strength to strength.
15. “I have chosen to be cast away in the house of the Lord, rather than to dwell in the tents of sinners”. For he found the valley of weeping, he found humility by which he might rise: he knows that if he would raise himself he shall fall, if he humble himself he shall be exalted: he has chosen to be cast away, that he may be raised up. How many beside this tabernacle of the Lord's winepress, that is beside the Catholic Church, wishing to be lifted up, and loving their honours, refuse to see the truth. If this verse had been in their heart, would they not cast away honours, and run to the valley of weeping, and hence find in their heart the way of ascent, and hence go from virtues to virtue, placing their hope in Christ, not in some man or another? A good word is this, a word to rejoice in, a word to be chosen. He himself chose to be cast away in the house of the Lord; but He who invited him to the feast, when he chose a lower place calls him to a higher one, and says unto him, “Go up higher.” Yet he chose not but to be in the house of the Lord, in any part of it, so that he were not outside the threshold.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)