Putting aside theological considerations for the moment - what is the purpose of right and wrong? Humans are social animals. It appears that the bonds we make in families, tribes, nations etc are a very strong survival trait. Being immoral or breaking laws weakens those social bonds and is therefore selected against.
However this relatively recent biological imperative is at odds with a much older imperative: selfishness.
So why are some people more intrinsically kind and moral than others? The human brain is a complex thing. Subtle differences in structure can have profound affects on intelligence, personality, propensity, etc. Some people are born with a neural makeup that tends them more towards immorality and selfishness than the norm. Others are rewired that way by their experiences.
Edited by Dexx, : No reason given.