18 Be Jerusalem; remember of whom it is said, “Lord, in Your city their image You shall bring to nought.” These are they who now rejoice in such pomps; among them are they who have not come hither today because there is a show. To whom is it a gift? to whom is it a loss? Or why is it a gift? Why is it a loss? For not they only who exhibit such shows are smitten with loss, but with much greater loss are they smitten who delight in gazing on them. The former have their chest drained of its gold, the latter have their breast robbed of the riches of righteousness.
Most of the exhibiters of shows have to mourn for selling their estates; how ought the sinners to mourn, for losing their souls: Was it then for this that the Lord cried out on the Lord's Day, “Watch ye,” that today men should watch in this way. I beseech you, you citizens of Jerusalem, I beseech you by the peace of Jerusalem, by the Redeemer, the Builder, the Ruler of Jerusalem, that you address your prayers to God for them. May they see, may they feel, that they are trifling; and, intent as they are on the sights which please them, may at length look on themselves, and be displeased.
For in many we rejoice that this has already been done: and once we too sat there and were mad: and how many think we now sit there, who shall yet be, not only Christians, but also Bishops! From what is past, we conjecture what is to be: from what has already been done, we announce beforehand what God will do. Let your prayers be wakeful, you groan not for nothing. Certainly they who have already escaped, praying for those who are still in danger, because they too having been among those in danger, are heard; and God shall drag His people out of the captivity of Babylon; by all means He shall redeem and deliver them, and the number of the saints who bear the image of God shall be perfected....“Praise in unison,” because you consist of many: “praise,” because you have been made one. “We being many,” says the Apostle, “are one in Christ.” As then we are many, “we praise in unison;” as we are one, we “praise.”
The same are many and one, because He in whom they are one is ever One.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)