God told us in Scripture what He did. He's not imagining anything. He's CHOOSING to not remember our sins or credit them to our account.
When we repent and ask for forgiveness, God gives it to us. We die to self and become crucified in Christ, dead to sin, and are given new life in Christ. It is all IN Christ.
Colossians 3:3-4 3 For you have died, and your life is hidden with Christ in God. 4 When Christ who is your life appears, then you also will appear with him in glory.
If God is going to tell me He sees me with Christ's righteousness on me, I am not going to call Him a liar and tell Him he's wrong.
Are God and Christ not one in the same? Do you not believe that Jesus is God and Lord?
Peace be with you