Why is it bad to sin?

No, I don’t need you to explain why murder is wrong.

It makes sense to me that, if there is a benevolent God, then His word is final and we have to follow His rules. But why did He make some of those rules? If the Bible truly is the word of God, why is it so important to Him that we, for instance, refrain from cutting our hair in particular ways? Many of these rules seem very arbitrary. What does He think will happen if we do round the edges of our hair?

I am not trying to put down anyone’s beliefs. I truly want to know.