Another Mighty Mullet!
Like the young man pictured above, we all have things from our past we'd like to forget.  We struggle with God's forgiveness because we correctly assume we haven't earned it. Our sin is an offense to God; it violates His character, twists His words, stiffles His Spirit, and mocks His Law. We are by nature and by choice sinners- enemies of God...
The Apostle Paul writes in Romans chapter 5 that "while we were weak (read ; powerless to address our problem - sin), Christ died for the ungodly."  Ungodly... that's a terrible word, but it describes exactly what we were before Christ saved us. Paul continues, "but God shows His love for us in that while we were still sinners, Christ died for us." Jesus didn't wait for me to turn over a new leaf or straighten up my act.... while I was STILL a sinner Christ died for me... That's grace! That's mercy!
The idea of grace is both appealing and appalling. We are drawn to its appeal because by believing Someone paid for my sin in my place is a revolutionary thought. Psalm 103:10 tells us that "He has not dealt with us according to our sins; i.e., He's not treated us as our sins deserve. Grace can also be appalling. Some people refuse God's grace because they don't think they need it. They pay their own way. In accepting grace, we must admit that we need it.... this can be and should be very humbling. To say that we aren't good enough is a tough pill to swallow, but it is the medicine we MUST take in order to have grace. When we think we are good enough or that we measure up or that we are better than most people we know, we are in essence, deciding to be our own god. Accepting God's grace is the belief that your sins were placed on Christ at the cross (Isaiah 53:4-6). He was punished in your place! Believe it and be saved!!
Back to the picture- and your past; Isaiah 43:25 tells us that God, for HIS OWN SAKE (not our goodness) blots out our past record and remembers our sin no more..
God deliberately choses NOT to remember!
"My  sin, O the bliss of this glorious thought;
My sin, not in part, but the whole;
Is nailed to the cross and I bear it no more;
Praise the Lord! Praise the Lord! O my soul!"  - Horatio Spafford, 1873