We invented God and the law of karma etc. to protect weaker people from the wrath of the powerful. If there would be God living in some heaven and maintaining the ledger of our deeds, then it would have been impossible for him to punish each and every sinners on the day of judgement. Why would a sane and wise entity allow humans to accumulate sins? Won't he punish the sinners when they were committing a felony? What is the purpose of punishment if the guilty person has forgotten everything about the incident?
This is nothing but a clever method to keep people away from bad deeds. Hence, self realization, mutual co-operation, curtailment of bad things and bad people is the only solution for us.