Q. 40 What did God at first reveal to man for the rule of his obedience?A. The rule which God at first revealed to man for his obedience, was the moral law.Everyone has a moral nature like this from creation (Rom 

-15). Gentiles have a moral nature even though they do not have the written law (v. 14). They have the work of the law written in their hearts (v. 15). We really can't get away from morality even if we want to. If we were not moral, anything would go… but nobody accepts that!

WSC Q41: The Summary of the Moral Law

The idea of imparting a body of truth (rudiments of the faith) is found repeatedly in scripture under many different terms and descriptions. We are not given a complete catechism or confession in the Bible. That is because we are to write our own according to the needs of the day. They must refute new heresies as they arise. Our Lord has called us to catechise in His church… to teach disciples the basics of the faith. Make the most of this instruction: memorise your Catechism, listen to the messages, and pray for the Spirit to work.