Because the only sin which God does not forgive is our lack of forgiveness of others (Mt 6:14).
لا تياسىىىىىىىىىىىىىىىىىىىىىىىىىىىىىىىىىىىىىىىىىىىىىى ىىىىىىىىىىىىىىىىىىىىىىىىىىىىىىىىىىىى فرج الله قريب من غير عمليات