Doing the right thing gives no credit to our bankrupt account, because we should be doing good anyway, as much as we can.
Only the unmerited favour of God in Jesus, whose goodness was credited to our account, can take us out of the red.
Sin is not canceled by lawful living, for no person is able to live up to the Law. The Law reveals guilt, fills the conscience with terror, and drives men to despair. Much less is sin taken away by man-invented endeavors. The fact is, the more a person seeks credit for himself by his own efforts, the deeper he goes into debt. Nothing can take away sin except the grace of God. In actual living, however, it is not so easy to persuade oneself that by grace alone, in opposition to every other means, we obtain the forgiveness of our sins and peace with God.
– Martin Luther, Commentary on Galatians 1:3)