6 But now what? “The earth has flowed down”. If the earth has flowed down, whence has it flowed down except by sins? Therefore also they are called delinquencies. To delinquish is as it were by a kind of liquidity to slip down from the stability of firmness in virtue and righteousness. For it is through desire of lower things that every man sins: as he is strengthened by the love of higher things, so he falls down and as it were melts away by desire of lower things.
This flux of things by the sins of man the merciful forgiver observing, being a merciful forgiver of sins, not yet an exactor of punishments, He observes and says: The earth herself indeed has flowed down by them that dwell in her. That which follows is an exposition, not an addition. As though thou were saying, in what manner has the earth flowed down? Have the foundations been withdrawn, and has anything therein been swallowed up in a sort of gulf? What I mean by earth is all they that dwell therein.
I have found, he says, the earth sinful. And I have done what? “I have strengthened the pillars thereof.” What are the pillars which He has strengthened? Pillars He has called the Apostles. So the Apostle Paul concerning his fellow-Apostles says, “who seemed to be pillars.” And what would those pillars have been, except by Him they had been strengthened? For on occasion of a sort of earthquake even these very pillars rocked: at the Passion of the Lord all the Apostles despaired.
Therefore those pillars which rocked at the Passion of the Lord, by the Resurrection were strengthened. The Beginning of the building has cried out through the pillars thereof, and in all those pillars the Architect Himself has cried out. For the Apostle Paul was one pillar of them when he said, “Would ye receive a proof of Him that speaks in me— Christ?” Therefore, “I,” he says, “have strengthened the pillars thereof:” I have risen again, I have shown that death is not to be feared, I have shown to them that fear, that not even the body itself does perish in the dying.
There terrified them wounds, there strengthened them scars. The Lord Jesus could have risen again without any scar: for what great matter were it for that power, to restore the frame of the body to such perfect soundness, as that no trace at all of past wound should appear? He had power whence He might make it whole even without scar: but He willed to have that whereby He might strengthen the rocking pillars.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)