Catechisma

Q40. What did God first reveal to humanity as the rule of obedience?

The rule that God first revealed to humanity for obedience was the moral law.

Scripture Proofs — King James Version

1

Romans 2:14–15

For when the Gentiles, which have not the law, do by nature the things contained in the law, these, having not the law, are a law unto themselves: Which shew the work of the law written in their hearts, their conscience also bearing witness, and their thoughts the mean while accusing or else excusing one another;)

Romans 10:5

For Moses describeth the righteousness which is of the law, That the man which doeth those things shall live by them.