Hang on chakka. Not sure you've understood the concept of 'he died for our sins'.
The Christian thinkers, such as the Jesuits,and the clergy, think about it and understand what it means. Let's hope that the congregation understand it but, if they don't, that doesn't mean its not sound.
The Lord's prayer asks God to forgive us our trespasses just as we forgive them that trespass against us. You may feel that the second part is something of a hopeful statement. We patently don't do so with practical results; the man who is stabbed by another may forgive his assailant, but the assailant still goes to jail. But it may make a Christian feel better if he forgives and forgets and he may hope that God will do the same. No good dying and finding there are convictions which aren't spent, as it were, that God hasn't forgiven.
The fact that atheists, including me, think that all religions based on some deity's existence are wrong, since there is no deity, doesn't affect the internal logic of the religion