22 And how is it declared? “In the nations gathering together in one, and the kingdoms, that they may serve the Lord”. How is this accomplished, unless by the blood of the slain? How accomplished, but by the groans of the fettered? Those therefore who were in tribulation and humility have been heard; that in our times the Church might be in the great glory which we see her in, so that the very kingdoms which then persecuted her, now serve the Lord.
23. “She answered Him in the way of His strength”....The preceding words show, that either “His praise,” or “Jerusalem,” answered: for it was said, “And His praise in Jerusalem; in the nations gathering together in one, and the kingdoms, that they may serve the Lord. Respondit ei.” We cannot say, “the kingdoms answered,” for he would have said responderunt. Respondit ei. We cannot say, “the nations answered,” for he would have said, responderunt (in the plural). Since then it is Respondit ei, in the singular, we look for the singular number above, and find that the words, “His praise,” and “Jerusalem,” are the only words in which we find it. But since it is doubtful, whether it be “His praise,” or “Jerusalem,” let us expound it each way. How did “His praise” answer Him? When they who are called by Him thank Him. For He calls, we answer; not by our voice, but by our faith; not by our tongue, but by our life....From His elect and holy men, Jerusalem also answers Him. For Jerusalem also was called: and the first Jerusalem refused to hear, and it was said unto her, “Behold, your house shall be left unto the desolate.”...But that Jerusalem, of whom it was written, “Sing, O barren, you that did not bear,” “She has answered Him.” What means, “She has answered Him”? She despises Him not when He called. He sent rain, She gave fruit.
24. “She answered Him:” but where? “in the path of His strength.”...The Church therefore answered Him not in the way of weakness; because after His resurrection He called the Church from the whole world, no longer weak upon the cross, but strong in heaven. For it is not the praise of the Christian faith that they believe that Christ died, but that they believe that He arose from the dead. Even the Pagan believes that He died; and makes this a charge against you, that you have believed in one dead. What then is your praise? It is that you believe that Christ arose from the dead, and that thou dost hope that you shall rise from the dead through Christ: this is the praise of faith. “For if you shall confess with your mouth that Jesus is the Lord, and shall believe in your heart that God has raised Him from the dead, you shall be saved.”...This is the faith of Christians. In this faith then, in which the Church is gathered, “She has answered Him,” She gave Him worship according to His commandments: “in the path of His strength,” not in the path of His weakness.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)