What did God at first reveal unto man as the rule of his obedience?

The rule of obedience revealed to Adam in the estate of innocence, and to all mankind in him, beside a special command not to eat of the fruit of the tree of the knowledge of good and evil, was the moral law.

Scripture Proofs

Gen. 1:26-27; Rom. 2:14-15; Rom. 10:5; Gen. 2:17