That statement causes me to ask two more questions. I believe that without God a person cannot answer either of these questions. Let me take them one by one. We humans don't need God because we can use our reason to decide right from wrong. We can use reason as a judge of the natural feelings and instincts we have.
Reason can sort out which are good and which are bad.
However, I could ask where we got reason from. If there is no God, our neurons and the way they are arranged all come from evolution. But let's assume our reasoning powers are satisfactory. If they aren't, there's no way we can figure that out, and we have to do the best we can with what we've got, I guess. Immanuel Kant and other philosophers during the Enlightenment believed that humans could arrive at an ethical code solely through the use of reason and logic.