The biggest reason we have trouble believing God when he says he’s going to forgive us is that we confuse God’s forgiveness with the forgiveness of people. And there’s a big difference. For instance, people are often reluctant to forgive. Psalm 86 says “You are kind and forgiving O Lord abounding in love to all who call to you.”
People forgive but they don’t forget and so when you get into one of these heated arguments, they have to throw your past transgressions back at you to gain a strategic advantage. Yet the Lord says in Isaiah 43 “I, even I, am he who blots out your transgressions for my own sake and remembers your sin no more.”
People forgive minor annoyances but sometimes are reluctant to forgive major hurts. Isaiah chapter 1 says “Though your sins are like scarlet, they shall be white as snow. Though they are red as crimson, they shall be like wool.”
People sometimes put conditions on their forgiveness but not God. Isaiah 55 says “Let the wicked forsake his way and the evil man his thoughts. Let him turn to the Lord and he will have mercy on him and to our God, for he will freely pardon.”
People may forgive one or two mistakes but then they draw the line. They say “That’s it, no more.” However, Lamentations chapter 3 says “Yet this I call to mind and therefore I have hope because of the Lord’s great love, we are not consumed, for his compassions never fail, they are new every morning. Great is your faithfulness.”
So you see it’s clear that God’s forgiveness is not like human forgiveness. Its scope, its completeness, its availability far outstrip the ability of people to forgive. Whatever it is you’ve done, listen to the words of 1 John 1:9 “If we confess our sins, God is faithful and just and will forgive us our sins and purify us from all unrighteousness.”