3 “You have known My down-sitting and Mine up-rising”. What here is “down-sitting,” what “up-rising”? He who sits, humbles himself. The Lord then “sat” in His Passion, “up-rose” in His Resurrection. “You,” he says, hast known this; that is, You have willed, You have approved; according to Your will was it done. But if you choose to take the words of the Head in the person of the Body: man sits when he humbles himself in penitence, he rises up when his sins are forgiven, and he is lifted up to the hope of everlasting life. Lift not up yourselves, unless you have first been humbled. For many wish to rise before they have sat down, they wish to appear righteous, before they have confessed that they are sinners....
Source: The Enarrations, or Expositions, on the Psalms (New Advent)