13 “He shall judge among the heathen: He shall fill up what has fallen”. Whoever you are who art obstinate against Christ, you have raised on high a tower that must fall. It is good that you should cast yourself down, become humble, throw yourself at the feet of Him who sits on the right hand of the Father, that in you a ruin may be made to be built up. For if you abide in your evil height, you shall be cast down when you can not be built up. For of such the Scripture says in another passage: “Therefore shall He break down, and not build them up.” Beyond doubt he would not say this of some, unless there were some whom He broke down so as to build them up again.
And this is going on at this time, while Christ is judging among the heathen in such a manner as to fill up what has fallen. “He shall smite many heads over the earth.” Here upon the earth in this life He shall smite many heads. He makes them humble instead of proud; and I dare to say, my brethren, that it is more profitable to walk here humbly with the head wounded, than with the head erect to fall into the judgment of eternal death. He will smite many heads when he causes them to fall, but He will fill them up and build them up again.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)