God has forgiven us through the finished work of Jesus.  This is a wonderful truth for every believer.  God has forgiven us the penalty of sin.  God forgives us when we as believers occasionally sin against him.  We have been cleansed out from sin through the shed blood of Jesus.  This no mere intellectual doctrine it is a living reality for us.  Jesus has set us free.  Therefore when others sin against us we are to set them free too.