With voices in harmony and hearts in concord we have begged the Lord for our own hearts by saying, Create a clean heart in me, O God, and renew an upright spirit in me (Psalm 51:12)…
It’s a psalm of someone repenting, someone wishing to retrieve the hope he had lost, lying where he had fallen, begging the Lord to give him a hand to raise him up again; like someone quite capable of injuring himself but not of healing himself. After all, we can stab and wound our own flesh whenever we want, but to heal it we look for a doctor; well, in the same way the soul is perfectly able to sin all by itself, but to heal the hurt it has caused by sinning, it implores the helping hand of God.
That’s why he says in another psalm, I myself have said it, Lord. Have mercy on me, heal my soul since I have sinned against you (Psalm 41:5). The reason he says I myself have said it, Lord, is to thrust before our eyes the fact that the will and decision to sin arises from the soul and that we are fully capable of destroying ourselves, while it takes God to seek that which was lost and to save that which had wounded itself. For the Son of Man has come to seek and save that which was lost (Luke 19:10). It is to him that we pour out our prayers and say Create a clean heart in me, O God, and renew an upright spirit in me (Psalm 51:12). Le the soul that has sinned say this, or it may perish twice over through despair, having lost itself once already by its delinquency.
St. Augustine of Hippo