Romans 2:15

As much as some may pretend that there is no right and wrong, there are certain things we all agree are inappropriate. Natural law is in our hearts though we have the free will to accept or ignore it. Paul was writing long before the scientific method was developed and used on humans to test whether there are underlying principles that guide what we think distinguish a right action from a wrong action, yet modern studies continue to show that there are understandings that would consistently guide our conscience if we would left them, regardless of our race, nationality, religion, age, or other factors. God is just: He won't expect us to live by a Law we don't know. Yet He has put a law in our hearts and when we willfully choose to disobey Him, it is perfectly just for Him to judge us according to that law.