God Has A Bad Memory
God is all-knowing. This means that we keep no secrets from our Heavenly Father, even the ones we don't tell ourselves. His memory is perfectly clear, yet he can wipe out any of our repented sins.
What's really cool is that our Savior separates our sins from us. We are no longer tainted by that mistake.
God is omniscient.
He has total recall.
God is merciful.
He cannot remember our repented sins.
All we have to do is ask.
"God has promised forgiveness to your repentance, but He has not promised tomorrow to your procrastination."--Augustine