Q. What did God reveal to man for the rule of his obedience?  

A. The rule which God first revealed to man for his obedience, is the moral law, which is summarized in the Ten Commandments.

Deuteronomy 10:4 And He wrote on the tablets according to the first writing, the Ten Commandments, which the LORD had spoken to you in the mountain from the midst of the fire in the day of the assembly; and the LORD gave them to me.