'善有善报' means:
If you are friendly to others, others will do the same to you.
People will help you because of your kindness when you are in trouble.
So good is rewarded.
That is generally known as "The Golden Rule". It appears in most major religions in one form or another. I think the idea is older than any existing religion, but I can't substantiate that.
It is an apt description of how to elicit desirable behavior from most other people. There ae always exceptions. Not everyone is nice and not everyone is empathetic. Luckily sociopaths and psychopaths are a very small fraction of the world's population.