Several Bible passages warn that God’s memory is complete with respect to people’s sins, even with respect to their thoughts (Hebrews 4:13). However, God apparently wants to forget the sins He has forgiven; indeed, He claims to do se here.
Though God has no no need to clean His mind of hurtful thoughts, we might understand this divine promise better if we compared it to washing our own minds of images and memories that cause us sadness or remind us of defeat and gloom. While we can redirect anger and melancholy, we cannot erase memories. But God apparently wants to and does so-ridding Himself of memories of the pain and wretchedness of sin.
HEBREWS 8:12 – 12 For I will be merciful to their unrighteousness, and their sins and their iniquities will I remember no more.