20 If therefore You are “true,” “Look upon me, and have mercy upon me: give power unto Your servant.” Because You are “true,” “give power unto Your servant”. Let the time of patience pass away, the time of judgment come. How, “give power”? The Father judges no man, but has committed all judgment unto the Son. He rising again will come even to earth Himself to judge: He will appear terrible who appeared despicable. He will show His power, who showed His patience; on the Cross was patience; in the judgment will be power. For He will appear as Man judging, but in glory: because “as you saw Him go,” said the Angels, “so He will come.” His very form shall come to judgment; therefore the ungodly also shall see Him: for they shall not see the form of God. For blessed are the pure in heart, for they shall see God....In the vision of the Father there is also the vision of the Son: and in the vision of the Son there is also the vision of the Father. Therefore He adds a consequence, and says: “Do you not know that I am in the Father, and the Father in Me?” that is, both in Me seen the Father is seen, and in the Father seen the Son too is seen. The vision of the Father and the Son cannot be separated: where nature and substance is not separated, there vision cannot be separated. For that you may know that the heart ought to be made ready for that place, to see the Divinity of the Father and Son and Holy Spirit, in which though not seen we believe, and by believing cleanse the heart that there may be able to be sight: the Lord Himself says in another place, “He that has My commands and keeps them, he it is that loves Me: and he that loves Me shall be loved by My Father: and I will love him, and will manifest Myself unto him.” Did they not see Him, with whom He was talking? They both saw Him, and did not see Him? They saw something, they believed something: they saw Man, they believed in God. But in the Judgment they shall see the same Lord Jesus Christ as Man, together with the wicked: after the Judgment, they shall see God, apart from the wicked.
21. “And save the Son of Your handmaid.” The Lord is the Son of the handmaid. Of what handmaid? Her who when He was announced as about to be born of her, answered and said, “Behold the handmaid of the Lord: be it unto me according to Your word.” He saved the Son of His handmaid, and His own Son: His own Son, in the Form of God; the Son of His handmaid in the form of a servant. Of the handmaid of God, therefore, the Lord was born in the form of a servant; and He said, “Save the Son of Your handmaid.” And He was saved from death, as you know, His flesh, which was dead, being raised again....And each several Christian placed in the Body of Christ may say, “Save the Son of Your handmaid.” Perhaps he cannot say, “Give power unto Your servant:” because it was He, the Son, who received power. Yet wherefore says He not this also? Was it not said to servants, “You shall sit upon twelve thrones, judging the twelve tribes of Israel”? and the servants say, “Do you not know that we shall judge Angels?” Each one therefore of the saints receives also power, and each several saint is the son of His handmaid. What if he is born of a pagan mother, and has become a Christian? How can the son of a pagan be the son of His handmaid: He is indeed the son of a pagan mother after the flesh, but the son of the Church after the Spirit.
22. “Show me a sign for good”. What sign, but that of the Resurrection? The Lord says: “This wicked and provoking generation seeks after a sign; and there shall no sign be given it, but the sign of the Prophet Jonah.” Therefore in our Head a sign has been shown already for good; each one of us also may say, “Show me a sign for good:” because at the last trumpet, at the coming of the Lord, both “the dead shall be raised incorruptible, and we shall be changed.” This will be a sign for good. “That they who hate me may see it, and be ashamed.” In the judgment they shall be ashamed unto their destruction, who will not now be ashamed unto their healing. Now therefore let them be ashamed: let them accuse their own ways, let them keep the good way: because none of us lives without being ashamed, unless he first be ashamed and live anew. Now God grants them the approach of a healthy shame, if they despise not the medicine of confession: but if they will not now be ashamed, then they shall be ashamed, when “their iniquities shall convince them to their face.” How shall they be ashamed? When they shall say, “These are they whom we had sometimes in derision, and a parable of reproach. We fools counted their life madness: how are they numbered among the children of God! What has pride profited us?” Then shall they say this: let them say it now, and they say it to their health. For let each one turn humbly to God, and now say, What has my pride profited me? And hear from the Apostle, “For what glory had ye in those things of which you are now ashamed?” You see that there is even now a wholesome shame while there is a place of penitence: but then one which will be late, useless, fruitless....
Source: The Enarrations, or Expositions, on the Psalms (New Advent)