"do not..."

Sometimes you are told not to do something, fight the temptation of acting in a specific manner. You give your best to accomplish that and in the end you figure out that it's not enough.
It's not enough not to do the thing called bad. Not to do means doing exactly the opposite thing, take action in a different way and not just stopping the bad stuff. Simply not doing means that you not exist, is exactly like you haven't lived in that given time.

What happens if instead of only stopping it you also do something called good?

It's not only about your relation with another human been, it also regards your inner self, your religious life, you entirely: just not doing it's the same as you weren't there; adding the right action makes you alive in that moment of time.