In general there will be good results and outcomes to good deeds because majority of the people around reciprocate to good behaviour, kindness, caring, service and contribution. But evolutionary millions of yours back when the environment is dangerous and uncertain we humans were living based on our survival mechanisms and we must be living in the fight and flight mode for the majority of the times. There has to be a motivation that acts as a deterrent to enable good behaviour and prevent from doing immoral and bad activities.
We humans need a strong motivation to do something that is difficult, challenging which may not have guaranteed returns but risk associated with it. When we create a higher power that always looks after people who does good things and helps people who does positive contributions then at least for few people have a clear direction towards which they need to move for welfare of the society.
Morals, ethics, principles, being honest, sincere, trustworth, reliable, integrity, being responsible, caring, disciplined, accountable, committed, being brave, courageous are the traits that one needs to have regardless of getting good returns or not. They cannot be dependent of reward or punishment. They are noble causes to live for by themselves whether one believes God or not.
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