4 Who is “our God,” that praise should be pleasant to Him? He makes Himself sweet to us, He commends Himself to us; thanks to His condescension....“But God commends His love to us”...“in that, while we were yet sinners, Christ died for us.”...Let us see whether it be the commendation which the Apostle speaks of, that Christ died for the sinners and ungodly: “the Lord who builds up Jerusalem, and gathers the dispersions of Israel”. For the people of Jerusalem are the people of Israel.
It is Jerusalem “eternal in the heavens,” whereof the Angels are citizens also....All the citizens then of that city, through “seeing God,” rejoice in that great and wide and heavenly city; they gaze upon God Himself. But we are wanderers from that city, driven out by sin, that we should not remain there; weighed down by mortality, that we should not return there. God looked back on our wandering, and He who “builds up Jerusalem,” restored the part that had fallen. How restored He the part that had fallen?...He sent then to our captive estate His Son as a Redeemer.
Take with You, said He, a bag, bear therein the price of the captives. For He put on Him our mortal flesh, and therein was the Blood, by the shedding of which we were to be redeemed. With that Blood He “gathered the dispersions of Israel.” And if He gathered them that before were dispersed, how must we strive that they be gathered who now are dispersed? If the dispersed have been gathered, that in the Hand of the Builder they might be fashioned into the building, how should they be gathered who through disquiet have fallen from the Hand of the Builder? Behold whom we praise; behold to whom we owe praise all our life long.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)