Regret

You and I must never look at our past lives; we must never look at any sin in our past life in any way except that which leads us to praise God and to magnify His grace in Christ Jesus… When Paul looks at the past and sees his sin he does not stay in a corner and say, “I am not fit to be a Christian, I have done such terrible things.” Not at all. What it does to him, its effect upon him, is to make him praise God. He glories in grace and says, “And the grace of our Lord was exceedingly abundant with faith and love which are in Christ Jesus.

Martyn-Lloyd-Jones