Overview

The catechism now turns from faith (what we believe about God, Q4–38) to duty (what God requires, Q39–107). This section opens the “duty” half: the rule of obedience is the moral law (Q39–40), summarized in the Ten Commandments (Q41), whose sum is love to God and neighbor (Q42), and introduced by a preface (Q43–44). It is the gateway to the exposition of each commandment that follows.

The Questions & Answers

Q39. What is the duty which God requireth of man? A. The duty which God requireth of man, is obedience to his revealed will.

Scripture Proofs (ESV):

“And what does the LORD require of you but to do justice, and to love kindness, and to walk humbly with your God?” (Mic. 6:8, ESV)

Further proofs: 1 Sam. 15:22; Deut. 29:29; Luke 10:26–28.

Q40. 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.

Scripture Proofs (ESV):

“For when Gentiles, who do not have the law, by nature do what the law requires… They show that the work of the law is written on their hearts.” (Rom. 2:14–15, ESV)

Further proofs: Rom. 10:5; Luke 10:27.

Q41. Where is the moral law summarily comprehended? A. The moral law is summarily comprehended in the ten commandments.

Scripture Proofs (ESV):

“And he declared to you his covenant, which he commanded you to perform, that is, the Ten Commandments, and he wrote them on two tablets of stone.” (Deut. 4:13, ESV)

Further proofs: Matt. 19:17–19; Exod. 20:1–17; Deut. 10:4.

Q42. What is the sum of the ten commandments? A. 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.

Scripture Proofs (ESV):

“You shall love the Lord your God with all your heart and with all your soul and with all your mind… You shall love your neighbor as yourself.” (Matt. 22:37–40, ESV)

Further proofs: Mark 12:30–31; Rom. 13:9–10; Gal. 5:14.

Q43. What is the preface to the ten commandments? A. The preface to the ten commandments is in these words, I am the Lord thy God, which have brought thee out of the land of Egypt, out of the house of bondage.

Q44. What doth the preface to the ten commandments teach us? A. The preface to the ten commandments teacheth us, That because God is the Lord, and our God, and Redeemer, therefore we are bound to keep all his commandments.

Scripture Proofs (ESV):

“And God spoke all these words, saying, ‘I am the LORD your God, who brought you out of the land of Egypt, out of the house of slavery.’” (Exod. 20:1–2, ESV)

Further proofs: Lev. 18:30; 19:37; Luke 1:74–75; 1 Pet. 1:15–18.

Exposition: Q39 defines duty simply as “obedience to his revealed will” — not our own ideas of goodness. Q41 locates the moral law’s summary in the Ten Commandments, and Q42 distills the Ten to their essence: love to God (the first four, the “first table”) and love to neighbor (the last six, the “second table”). This love-frame governs everything: every command is an expression of love. Q43–44 are vital: the law begins with grace. Before God commands anything, He declares, “I am the LORD your God… your Redeemer” — He redeemed Israel from Egypt before giving the law. So obedience flows from redemption, not toward it. We keep His commandments not to earn His favor but because He is already our Lord, God, and Redeemer.

Connections

• WLC Q91–98 — the duty God requires; the moral law; the sum of the Ten Commandments; the preface; the rules for understanding the commandments.
• WCF 19 (Of the Law of God) — the moral, ceremonial, and judicial law, and the right use of the moral law for believers.
• Loci: The moral law; the two tables; the third use of the law; law and gospel.

Pastoral & Practical Significance

The order of these questions guards the gospel even as the catechism turns to duty. The preface (Q43–44) is the key to keeping the commandments from becoming a ladder of works-righteousness: God redeems first, then commands. The Ten Commandments were given to a people already rescued, as the shape of grateful love, not the price of acceptance. So when you read “Thou shalt” and “Thou shalt not” in the following sections, hear them as the loving direction of your Redeemer, not the threats of a taskmaster. And Q42 keeps the whole law from fragmenting into a checklist: every command is an expression of love — to God and neighbor. If love is the sum, then obedience is never mere external conformity but the engagement of the heart. The law, rightly framed by grace, becomes a delight (Ps. 119:97) rather than a burden.

For Memory & Reflection

• Memorize Q42 (the sum of the law), Q43 (the preface), and Q44; anchor verses: Matthew 22:37–40 and Exodus 20:1–2.
• The law begins with grace (“I am… your Redeemer”). How does that change the way I hear God’s commands?
• If love is the sum of all the commandments, where is my obedience merely external, lacking love?