The Shorter Catechism-Division III-What We Are To Do.
I. The Moral Law: Q & A 39-44
Q. 39 What is the duty which God requires of man?
A. 39 The duty which God requires of man is obedience to His revealed will.
This section, and this question in particular, takes us back to the start of the Catechism, where we are to understand that the first axiom of all thought and existence is the word of God. What we do is based upon and is made possible, only because of what God has done for us. “Fear God and keep His commandments, for this is man’s all” (Eccl. 12:13 Cf. Mic. 6:8).
Q. 40 What did God at first reveal to man for the rule of his obedience?
A. 40 The rule which God at first revealed to man for his obedience, was the moral law.
Q. 41 Where is the moral law summarily comprehended?
A. 41 The moral law is summarily comprehended in the ten commandments.
Q. 42 What is the sum of the ten commandments?
A. 42 The sum of the ten commandments is, to love the Lord our God with all our heart, with all our soul, with all our strength, and with all our mind; and our neighbour as ourselves.
Q. 43 What is the preface to the ten commandments?
A. 43 The preface to the ten commandments is in these words, “I am the LORD your God, who brought you out of the land of Egypt, out of the house of bondage.”
Q. 44 What does the preface to the ten commandments teach us?
A. 44 The preface to the ten commandments teaches us, that God is the LORD, and our God, and Redeemer, therefore we are bound to keep all His commandments.
This moral law is a law which is revealed to all humanity (Rom. 2:14-15). However, it finds its fullest and clearest expression in the ten commandments (Dt. 10:4 Cf. Mt. 19:17). Jesus reiterated the Old Testament emphasis first on God then on one’s neighbour, summarizing not only the ten commandments, but the whole of the scriptures as “the law and the prophets” (Mt. 22:37-40). This is also what it means to love (Rom. 13:10). The preface to the ten commandments shows us that this duty is in response to the redemption which God has procured for us (Ex. 20:2).
In Deuteronomy Moses furthered this focus on the Covenant LORD as the redeemer of his people, by hearkening back to the covenant made at Horeb, and how Moses acted as a Mediator for them in the giving of the law, because they were afraid of the LORD’s voice. The preface teaches us that God is due this duty because He is our only sovereign covenant making and covenant keeping LORD, our redeemer (Cf. Dt. 24:18; II Cor. 5:15). As God’s people, we have been delivered from the bondage of sin to walk in newness of life, and the law is our standard of love toward both God and our fellow man.