What does it mean that God forgets our sin? Does He forget?

TL;DR:

God knows everything and does not forget past sin in the sense that He literally forgets. Instead, when one has been saved through Jesus, God removes all record of his or her guilt, never again remembering it with the intent of condemning the forgiven individual.

what does the bible say?

God is omniscient, meaning that He knows everything—there is nothing hidden from Him. However, Scripture also teaches that He “blots out” sin, expunging our record of wrongdoing. Because God knows everything, He does not forget sin in the sense that He doesn’t remember what we did. Instead, God chooses to not bring it up again. That is, once sin has been paid for, He no longer brings it to mind with the intent of declaring someone guilty. Because God is just, He cannot just ignore our sin. In order to “blot out” our sin, it must be paid for in full. He sent His Son, Jesus, for exactly this purpose. Jesus came and died in our place. For all who trust in Him, their sin has been paid, and God no longer holds them accountable—He has blotted their sin out of His record book.

from the old testament

What does it mean that God does not remember our sin? Does that mean He actually forgets what we have done? To answer that, we must first remember that God is omniscient. That means that He knows everything (Psalm 139:1–4). God knows everything, even our thoughts.
In Isaiah 43:25, the Lord says, “I, I alone, am the one who wipes out your wrongdoings for My own sake, and I will not remember your sins” (NASB). Some translations say that He “blots out” the sins like one would blot out a criminal’s record. God makes a conscious decision not to remember our sins. But it’s a particular kind of “not remembering”—it’s not remembering in the sense that He doesn’t bring them up to hold people guilty for them.
Psalm 103:12 says, “As far as the east is from the west, so far does he remove our transgressions from us.” There is an immeasurable distance from east to west because those directions stretch out infinitely. This poetically explains that when God “blots out” one’s sin, He completely removes it from His record keeping. It is no longer “on the books,” as it were.
Jeremiah gave a peek to Israel of how God could rightly remove sins that have not been punished: “For this is the covenant that I will make with the house of Israel after those days, declares the LORD: I will put my law within them, and I will write it on their hearts. And I will be their God, and they shall be my people… For I will forgive their iniquity, and I will remember their sin no more” (Jeremiah 31:33, 34b). While Israel did not know all the details about how God could be just and still forgive sin, God clearly promised that there would be a way and that it was connected with a heart change.

from the new testament

The author of Hebrews connected many Old Testament passages to Jesus, specifically the Old Testament sacrificial system. He quoted from the Jeremiah 31 passage, saying, “we have been sanctified through the offering of the body of Jesus Christ once for all… when Christ had offered for all time a single sacrifice for sins, he sat down at the right hand of God,… For by a single offering he has perfected for all time those who are being sanctified. And the Holy Spirit also bears witness to us; for after saying, ‘This is the covenant that I will make with them after those days, declares the LORD: I will put my laws on their hearts, and write them on their minds,' then he adds, 'I will remember their sins and their lawless deeds no more'” (Hebrews 10:10, 12, 14–17). In contrast to the Old Testament sacrifices that needed to be repeated every day, Jesus, the perfect lamb, only needed to die once because He was the perfect and complete sacrifice for mankind’s sins. He then resurrected and sat at the right hand of God. Through His death, all who believe are saved (“those who are being sanctified”).
God sent His Son, Jesus, to die for sinners (John 3:16).
Romans 3:23–25 tells us that God no longer remembers the sins of believers by counting them righteous. Their guilt is removed from His list of unpaid sins. He could do that because Jesus was “put forward as a propitiation” (v. 25). A propitiation is a sacrifice that appeases the wrath of God. When Jesus died, God poured out His judging wrath against Jesus for all who believe in Him.
So, God no longer remembers believers’ sin because the sins have already been paid for by Jesus. That means that God “forgets” them in the sense that He no longer holds the believer responsible for them. They are “off the books,” taken care of, finished (John 19:30).

implications for today

God knows everything, but He chooses not to hold someone accountable for sin when his or her penalty has already been paid. When He sent His Son, it was for the express purpose of dying as a propitiation, a sacrifice that would receive the Father’s full wrath for the sin of all who believe in Jesus. For those who trust in Jesus, God has blotted out their sin from the records.

For unbelievers, there really is only one implication: God currently is choosing to remember your sins! Since they have not (yet) been paid for, they remain on record. If you continue to reject Jesus, books listing your sins will be opened, and you will be judged and found guilty (Revelation 20:11–15). However, Jesus said that no one who comes to Him will be cast out (John 6:37b). That means that each person who genuinely repents of his or her sin and trusts in Jesus (Romans 10:9) will have every sin blotted out of the record books. Those sins will be forgotten and never brought up again because the penalty for them has already been paid by Jesus.

For believers, we must remember what God forgot! We don’t remember our past sins to dwell on what has been forgiven, but to remember just how great, kind, and gracious God is. Also, we remember that He continues to forgive. Though Jesus paid for all of your sins—past, present, and future—God wants you to grow in holiness and will discipline you when you sin (Hebrews 12:4–11). However, we are promised that every time we sin, if we repent, God is quick to forgive us (1 John 1:9).

understand

God does not literally forget sin but chooses never to recall it for condemnation.
All sin must be paid for, so God doesn’t forget our sin; He chooses to not remember it for those who trust in Him.
Jesus’s sacrifice covers the sin of those who trust in Him for salvation; in this way, God sees us as righteous.

reflect

What does it reveal about God's character that He chooses not to bring up forgiven sin again?
How does the reality that your sins are not counted against you as a believer affect your daily walk with Christ and your identity in Him?
How does remembering God's mercy for your past shape how you respond to your present struggles with sin?

engage

How can we explain the difference between God forgetting sin and God choosing not to remember it for condemnation?
What do God's justice and mercy in “blotting out” sin teach us about the cost of forgiveness through Jesus?
How can this truth—that God no longer holds believers accountable for sin—transform the way believers offer grace and accountability to one another?