WSC Q.40: What did God at first reveal to man for the rule of his obedience?
The rule which God at first revealed to man for his obedience, was the moral law. (Rom. 2:14–15, Rom. 10:5)
WLC Q.92: 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, besides a special command not to eat of the fruit of the tree knowledge of good and evil, was the moral law. (Gen. 1:26–27, Rom. 2:14–15, Rom. 10:5, Gen. 2:17)