So if God can forget those sins, why can’t we? Why do we still feel guilty? Let me offer a few brief reasons:
First, there is someone who doesn’t want us to feel the peace and joy of the Lord. The evil one hates the Lord and His people and stands as our accuser day and night. Many times when an old memory returns to your thoughts it is because the evil one wants to discourage you or move you to doubt the Lord and His love. In those times, you must cry out to the Lord for His strength and thank Him for His cleansing grace. Thank the Lord for the new life He has given you and praise Him for what He has done in your life. This is the way to resist the lies and the fears brought by the evil one. When we praise the Lord for His truth, the prince of liars will flee.
Another reason we cannot forget is that there are often continuing consequences for our sins. The Bible never suggests that we will suddenly be free from all earthly consequences when we turn to the Lord. Sometimes that is given as a special gift from God, but usually not. If you signed for a loan you should not have gotten, you are still liable to repay that loan even if you repent of the sin. If you committed a crime, you may still have to suffer the earthly punishment for that crime. Some people see the consequences of their sin every day. No wonder they remember.
But listen: Just because you have continuing consequences does not mean that you are not forgiven! Those continuing consequences are things the Lord has built in your life for His purpose. They are reminders, perhaps, of how much He loves you.
How is that? Well, I would suggest that any reminder of the past sins should move us to give thanks to the Lord for His forgiveness. Consider those things memorial stones set in your life to give witness to what He has done. Use those reminders as motivation to praise Him all day long.
So, you see, you are a new creature in Christ. The person who did those things died with Jesus on the cross. Now you are someone new, someone different. It is just as though you never did those things. Praise the Lord!