The phrase “forgive and forget” is not found in the Bible. However, there are numerous verses commanding us to “forgive one another” (e.g., Matthew 6:14 and Ephesians 4:32). A Christian who is not willing to forgive others will find his fellowship with God hindered (Matthew 6:15) and can reap bitterness and the loss of reward (Hebrews 12:14–15; 2 John 1:8).
Forgiveness is a decision of the will. Since God commands us to forgive, we must make a conscious choice to obey God and forgive. The offender may not desire forgiveness and may not ever change, but that doesn’t negate God’s desire that we possess a forgiving spirit (Matthew 5:44). Ideally, the offender will seek reconciliation, but, if not, the one wronged can still make a decision to forgive.
Of course, it is impossible to truly forget sins that have been committed against us. We cannot selectively “delete” events from our memory. The Bible states that God does not “remember” our wickedness (Hebrews 8:12). But God is still all-knowing. God remembers that we have “sinned and fall short of the glory of God” (Romans 3:23). But, having been forgiven, we are positionally (or judicially) justified. Heaven is ours, as if our sin had never occurred. If we belong to Him through faith in Christ, God does not condemn us for our sins (Romans 8:1). In that sense God “forgives and forgets.”
If by “forgive and forget” one means, “I choose to forgive the offender for the sake of Christ and move on with my life,” then this is a wise and godly course of action. As much as possible, we should forget what is behind and strive toward what is ahead (Philippians 3:13). We should forgive each other “just as in Christ God forgave” (Ephesians 4:32). We must not allow a root of bitterness to spring up in our hearts (Hebrews 12:15).
However, if by “forgive and forget” one means, “I will act as if the sin had never occurred and live as if I don’t remember it,” then we can run into trouble. For example, a rape victim can choose to forgive the rapist, but that does not mean she should act as if that sin had never happened. To spend time alone with the rapist, especially if he is unrepentant, is not what Scripture teaches. Forgiveness involves not holding a sin against a person any longer, but forgiveness is different from trust. It is wise to take precautions, and sometimes the dynamics of a relationship will have to change. “The prudent see danger and take refuge, / but the simple keep going and pay the penalty” (Proverbs 22:3). Jesus told His followers to “be as shrewd as snakes and as innocent as doves” (Matthew 10:16). In the context of keeping company with unrepentant sinners, we must be “innocent” (willing to forgive) yet at the same time “shrewd” (being cautious).
The ideal is for the offender to truly repent of the sin and for the offended to forgive and forget. The Bible tells us true repentance will result in a change of actions (Luke 3:8–14; Acts 3:19) and that love keeps no record of wrongs (1 Corinthians 13:5) and covers a multitude of sins (1 Peter 4:8). However, changing hearts is God’s business, and, until an offender has a true, supernatural heart change, it is only wise to limit the level of trust one places in that person. Being cautious doesn’t mean we haven’t forgiven. It simply means we are not God and we cannot see that person’s heart.