12 “But I,” for all drink, but separately I, that is, Christ with His Body, “for ever will rejoice, I will Psalm to the God of Jacob”: in that promise to be at the end, whereof is said, “corrupt not.” “And all the horns of sinners I will break, and there shall be exalted the horns of the Just”. This is, the one He humbles, the other He exalts. Sinners would not have their horns to be broken, which without doubt will be broken at the end. You will not have Him then break them, do thou today break them.
For you have heard above, do not despise it: “I have said to unjust men, Do not unjustly, and to the delinquents, Do not exalt the horn.” When you have heard, do not exalt the horn, you have despised and hast exalted the horn: you shall come to the end, where there shall come to pass, “All the horns of sinners I will break, and there shall be exalted the horns of the Just.” The horns of sinners are the dignities of proud men: the horns of the Just are the gifts of Christ. For by horns exultations are understood. You hate on earth earthly exultation, in order that you may have the heavenly.
You love the earthly, He does not admit you to the Heavenly: and unto confusion will belong your horn which is broken, just as unto glory it will belong, if your horn is exalted. Now therefore there is time for making choice, then there will not be. You will not say, I will be let go and will make choice. For there have preceded the words, “I have said to the unjust.” If I have not said, make ready an excuse, make ready a defence: but if I have said, seize first upon confession, lest you come unto damnation; for then confession will be too late, and there will be no defence.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)