This idea that we will forget our sins in heaven came up during the Sunday school today and I wasn't sure if this was something the American fundamentalist church held in common so I kept quiet so that I could look it up. Knowing that there's something wrong with that statement, just that I couldn't pin point what was wrong with it at the time.
After research, The PuritanBoard once again was helpful. John Calvin's too, on Isaiah 65:16-17.
I don't know why they would think that, as if being irresponsible is okay. No, we will remember our sins. What God meant was that we will not remember our sorrows, or the trouble of the past. Our eternal great joy in Heaven shall blot out the guilt, all negativity of our sins. The forgetfulness is the kind that by comparison it's like the Sun with its great light depriving the stars of their brightness, as Calvin puts it. Our memories of sins are not erased as if they were none existence to us. That is a kind of irresponsible thinking, and thus sinful.
Some from the PuritanBoard made useful comment on this:
If we praise Christ, the Lamb slain, how would we forget that slaying?
God has forgiven us completely and remembers not our debt. Meaning He does not call back the debt. Not that He has a blank in His memory about this.