If God would forgive all our sins now, then wouldn’t we continue sinning?
This is the funnest question of all. I love answering this one. See my post on justification and regeneration to see what I would recommend to be the answer.
Basically, a Muslim cannot accept the total forgiveness of all sin because it isn’t logical…according to his view of God and motivation for good works. According to the Muslim, the only thing that keeps him doing anything good is the idea that he may not be forgiven if he doesn’t make some effort to obey, make penance, appease wrath, etc. The only motivation he has to not live according to every lust of the flesh is that God reserves the right to send him to hell forever or not based on an arbitrary system of balances.
We understand that the motivation to do what’s right comes from a completely new heart with new desires when Christ lives within us. This is totally ununderstandable outside of being enlightened by the Word of God.