The virtue of slogans is brevity. Their vice is ambiguity. So they are risky ways of communicating. They are powerful and perilous. So we should exploit the power and explain the peril. – John Piper in Desiring God
The danger of a cliché or slogan is that they can make the unintelligent seam brilliant. This is often the route to accepting stupidity and heralding it as wisdom. I believe such to be the case with “forgive and forget.” Perhaps there is some individual who meant this simply to say that you must not bring up the incident of offence, that is, you refuse to prosecute anew. Alas if he could behold his cult. Humanly it is impossible to forget some things, especially the worst of things, the things that call for amazing forgiveness. To put such a burden upon a rape victim, or a molested child, and say that they have not truly forgiven their enemies unless they forget that wretched event is to play the Pharisee and heap heavy unbearable burdens upon such persons, a burden that they, if in the same position, surely could not, would not carry (Matthew 23:4).
“Ah, but God forgets! …Right?” This is the issue that I really want to address. God does not forget – ever! God does not forget – anything! He is omniscient; this is never compromised. God does not forget our sins, He remembered them on Jesus. He removes our sins, washes us from our sins, forgives us of our sins, and takes away our sins, but He does not forget them. If God could simply forget sin, what need is there for an atonement where sins are paid for? We wouldn’t need an atonement; God simply need perform a lobotomy on Himself.
On this John MacArthur said:
I’ve heard people suggest that God forgets our sins when He forgives. They usually cite Hebrews 10:17: ‘Their sins and their lawless deeds I will remember no more’ (cf. 8:12). Or Isaiah 43:25: ‘I, even I, am the one who wipes out your transgressions for My own sake, and I will not remember your sins.’
But those verses don’t say God forgets our sins. They say He will not remember them. What’s the difference? To forget something is to have no memory of it. Obviously God, who is omniscient, has not lost His memory of our transgressions. Rather, He refuses to call them to mind. He promises not to bring them up.
Wayne Grudem states:
Someone may object that God promises to forget our sins. For example, he says, ‘I will not remember your sins’ (Isa. 43:25). Yet passages like this can certainly be understood to mean that God will never again let the knowledge of these sins play any part in the way he relates to us: he will ‘forget’ them in his relationship to us. – in Systematic Theology
I’ll wrap this up by dealing with the two oft cited texts, Hebrews 10:17 and Psalm 103:12. In Hebrews 10 the single offering of Christ is being contrasted with the plethora of sacrifices under the Old Covenant. Under the old system there was a reminder for sins every year (Hebrews 10:3). Every year at the Day of Atonement all Israel was reminded of their sins. Now under Christ a decisive payment for sin has been made once for all. God will not bring our sins up against us because they have been paid for. This is not the language of memory loss, but redemption. When I pay a bill the creditor doesn’t remember it anymore, against me. This means not that they wiped every record it from their databases; but that they have marked it as paid. I don’t want to hear my creditor ever say they have lost record of previous bills, I want to hear them say they have received payment. I don’t want God to forget my sins, for all eternity I want the Son to remind Him that my sins are paid for.
Finally Psalm 103:12 says nothing about forgetting but removing. My sins are removed from me, where are they placed? Into some abyss of forgetfulness? No they are placed on Christ (2 Corinthians 5:17).
Again, God does not forget our sins, He remembered them all on Jesus, once for all.