Matthew 6:12 (NIV)
Forgive us our debts.
This may come as a shock to many believers, but we owe God a holy life. That is what we were created for, to be holy and perfect replicas of Him. When Adam and Eve sinned, they incurred the debt of sin and passed it on to us. God blesses holiness and judges sin. Holiness is a credit while sin is a debt. When the Lord taught us to pray, He was teaching us to ask God to forgive the debt of sin and grant us the credit (mercy) of holiness so that we no longer owe God. That is what Christ accomplished for us on the cross.