4 “In Your own righteousness deliver me, and save me”. Not in my own, but in Your own: for if in my own, I shall be one of those whereof he says, “Being ignorant of God's righteousness, and their own righteousness willing to establish, to the righteousness of God they were not made subject.” Therefore, “in Your own righteousness,” not in mine. For mine is what? Iniquity has gone before. And when I shall be righteous, Your own righteousness it will be: for by righteousness given to me by You I shall be righteous; and it shall be so mine, as that it be Yours, that is, given to me by You.
For I believe in Him that justifies an ungodly man, so that my faith is counted for righteousness. Even so then the righteousness shall be mine, not however as though my own, not as though by my own self given to myself: as they thought who through the letter made their boast, and rejected grace....It is a small thing then that thou acknowledge the good thing which is in you to be from God, unless also on that account thou exalt not yourself above him that has not yet, who perchance when he shall have received, will outstrip you.
For when Saul was a stoner of Stephen, how many were the Christians of whom he was persecutor! Nevertheless, when he was converted, all that had gone before he surpassed. Therefore say thou to God that which you hear in the Psalm, “In You I have hoped, O Lord, I shall not be confounded for everlasting: in Your own righteousness,” not in mine, “deliver me, and save me.” “Incline unto me Your ear.” This also is a confession of humility. He that says, “Incline unto me,” is confessing that he is lying like a sick man laid at the feet of the Physician standing. Lastly, observe that it is a sick man that is speaking: “Incline unto me Your ear, and save me.”
Source: The Enarrations, or Expositions, on the Psalms (New Advent)