Romans 2:13-15

13For it is not those who merely hear the Law [as it is read aloud] who are just or righteous before God, but it is those who [actually] obey the Law who will be justified [pronounced free of the guilt of sin and declared acceptable to Him].

14When Gentiles, who do not have the Law [since it was given only to Jews], do instinctively the things the Law requires [guided only by their conscience], they are a law to themselves, though they do not have the Law.

15They show that the essential requirements of the Law are written in their hearts; and their conscience [their sense of right and wrong, their moral choices] bearing witness and their thoughts alternately accusing or perhaps defending them