The Larger Catechism
91. Q. What is the duty which God requireth of man?
A. The duty which God requireth man, is obedience to his revealed will.
92. Q. What did God at first reveal unto man as the rule of his obedience?
A. 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.
Scriptural Defense and Commentary
 Romans 12:1-2. I beseech you therefore, brethren, by the mercies of God, that ye present your bodies a living sacrifice, holy, acceptable unto God, which is your reasonable service. And be not conformed to this world: but be ye transformed by the renewing of your mind, that ye may prove what is that good, and acceptable, and perfect, will of God. Micah 6:8. He hath showed thee, O man, what is good; and what doth the LORD require of thee, but to do justly, and to love mercy, and to walk humbly with thy God? 1 Samuel 15:22. And Samuel said, Hath the LORD as great delight in burnt offerings and sacrifices, as in obeying the voice of the LORD? Behold, to obey is better than sacrifice, and to hearken than the fat of rams.  Genesis 1:26-27. And God said, Let us make man in our image, after our likeness: and let them have dominion over the fish of the sea, and over the fowl of the air, and over the cattle, and over all the earth, and over every creeping thing that creepeth upon the earth. So God created man in his own image, in the image of God created he him; male and female created he them. Romans 2:14-15. For when the Gentiles, which have not the law, do by nature the things contained in the law, these, having not the law, are a law unto themselves: Which show the work of the law written in their hearts, their conscience also bearing witness, and their thoughts the mean while accusing or else excusing one another;) Romans 10:5. For Moses describeth the righteousness which is of the law, That the man which doeth those things shall live by them. Genesis 2:17. But of the tree of the knowledge of good and evil, thou shalt not eat of it: for in the day that thou eatest thereof thou shalt surely die.
Questions 91-148 thoroughly develop the contours of the moral law. For the most part, these questions explain what the Ten Commandments teach. However, questions 91-98 cover the idea of the “moral law.” Question 92 introduces it while question 93 answers the question, “What is the moral law?” The Heidelberg Catechism goes straight into asking, “What is the Law of God?” (#92) and the answer is the recitation of the Ten Commandments. It does not delve into the nature of what a “moral law” is. The Second Helvetic Confession (1566) explains the three-fold division of the law in Ch. 12 (“Of the Law of God”): moral, ceremonial, and judicial [civil] (“which is occupied about political and domestic affairs”). Our LC seems to develop these distinctions more thoroughly.
Yet concern about the “moral law” has interested many. In fact, many book have been written on “moral philosophy.” Yet these “theories” of right and wrong appear to be speculative to most simple and common sensed people. Their suspicions are well founded. Ethicists or academicians set aside some of the most common tenets and in turn argue for what most would consider vulgar and untenable. In a secular world, a firm and sure ethical system cannot be maintained. What makes what Hitler did right or wrong? Does might make right? Is my sense of “guilt” sociologically conditioned? Who can say this or that is wrong? Moral philosophers write volumes arguing for their method but
Philosophers, like Kant, offered what he thought was a very reasonable view of right and wrong (called “deontology”). We are to act from a sense of duty to what he called the “categorical imperative.” That is, we act according to that maxim which we can will would become a universal law. This vision in theory seems plausible providing everyone was perfectly reasonable and that our depraved nature would not impede or darken our understanding. Numerous other theories have been offered but the Christian looks at this differently.
We believe God exists, that He acted and acts in history, and most of all, that He has revealed (and reveals) Himself through the Scriptures.
Duty to God
“What is the duty which God requireth of man?” This answer assumes much. The catechism assumes the existence of God, the obligation of man, and the revelation of God. The fact of God’s revelation enables us to assume all three. God’s Word came to us and changed us and in turn we learn what He requires of us. The answer states, “The duty which God requireth man, is obedience to his revealed will.”
All the passages used to support the question (Rom. 12:1-2; Mic. 6:8; 1 Sam. 15:22) assume a covenantal context, that is, it assumes that God had already redeemed specific sinners (cf. Rom. 12:1-2, “by the mercies of God”; Mich 6:8, “with thy God”; 1Sam. 15:22, Samuel spoke these words to Saul, then King of Israel). This is reasonable. Only true believers, redeemed from their sin and darkness will acknowledge the Lord’s will for them. They only will bow to God since He lovingly redeemed them.
Yet, all creatures, because God created them, owe their obedience to His will. God will hold all men accountable to Himself (cf. 2Cor. 5:10). Man, as created and dependent beings, owe their entire existence to God and are obligated to their Creator. Vos says that “we are under moral obligation to love and serve him.”
Atheists deny this. They believe that man defines himself and no deity can demand obedience from him (“the divine command theory”). Most secular people, who at best are agnostic, for all intents and purposes, do not look to God for right and wrong. They either look to society or to their own gut level instincts.
God requires that we obey His revealed will. Again, this assumes God reveals and indeed, He has revealed His will clearly in His Word. Yet, Christians recognize a history of revelation has been given to them by God; that revelation has been written down in the Bible.
Moral Law and Adam
Before God’s revelation had been written down, God revealed Himself by speaking to His people. It began at creation. The question asks, “What did God at first reveal unto man as the rule of his obedience?” If in fact, man was obligated to obey God’s revealed will, then what was the very first revelation? “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.”
God spoke to Adam and specifically instructed him. Every believer recognizes that Adam received a special command to not eat of the tree of the knowledge of good and evil (Gen. 2:17). Yet, the divines also add that Adam was to obey “the moral law.” This may appear strange to Bible students who have not reflected on this point. God created Adam with a moral compass and enabled him to obey his creator. A “moral law” guided him.
The clearest biblical evidence for this is Romans 2:14-15: “For when Gentiles, who do not have the law, by nature do what the law requires, they are a law to themselves, even though they do not have the law. They show that the work of the law is written on their hearts, while their conscience also bears witness, and their conflicting thoughts accuse or even excuse them…” The law’s requirements (“work of the law” – τὸ ἔργον τοῦ νόμου), what they are to do (as in v. 14) is written on their hearts. Paul does not say that the law itself is written on their hearts (since this is a New Covenant blessing, Jer. 31:33) but rather its requirements: “Things required and stipulated by the law are written upon the heart.” The New Covenant promise meant more than a bare knowledge of the laws; rather, it enabled them to know God (v. 34) and walk according to His Word by the empowerment of the Spirit (see the New Covenant reference in Ezekiel, 36:27). So Rom. 2:14-15 clearly indicates God wrote the work of the law in man’s heart. We take this to be another way of saying that God wrote the moral law in man’s heart (“written on their hearts”).
G. I. Williamson offers an explanation as to what it was Adam knew and his statement is one of the best on this.
This does not mean that God gave Adam the law in an externally revealed and codified form. ‘For the law was given by Moses’ (John 1:17). Paul teaches us that the law was first transcribed in the human conscience (Rom. 2:14-15). It was ‘written in the hearts’ of men. This, however, does not mean that Adam was conscious of the Ten Commandments in the same way that we are. To us the law is a negative power which incites our enmity. In him it was a positive sense (perhaps like an intuition) which incited love of God and of good. But the difference was in Adam’s relation to the law, not the law itself.
Many of the Puritans argued that this moral law in Adam is the same as the Ten Commandments (cf. a Brakel): “…the law which is impressed upon man’s nature, is identical to the ten commandments, even though they are not equal in clarity.” Even if it could be argued that Adam did not labor under a Covenant of Works, the moral law still dictated his conduct. He was not created morally neutral. For example, his knowledge of his wife, her relation to him, etc. assume the sanctity of marriage and the moral laws governing marriage. Gen. 2:24 is something Adam himself understood. Murray says, “Verse 24 is an inference drawn from verse 23… [and] was known to Adam…” Jesus’ own statement teaches this when commenting on the implications of v. 24 (Mt. 19:5), “but from the beginning it was not so” (Mt. 19:8). That is, the teaching on marriage was from the beginning, at creation. It would be strange to argue that it was from the beginning and that Adam was the only one that did not understand it.
Why belabor this point? Why should we insist that the moral law existed in Adam? These three points may help us.
1. The moral law is not a strange new thing in God’s salvation history. It existed in Eden and expanded or was expounded it greater details later on redemptive history.
2. The moral law is not a “Mosaic” thing. The idea of law and obedience did not spring out of the Mosaic covenant. Adam was not “law-less.” A moral law governed his behavior.
3. The moral law is not arbitrary. The moral law declared in the OT were not “arbitrary” and restricted to ethnic Israelites. Its moral demands pertain to all human beings since it exists in all man (starting with Adam).
Watson says, “The end of our obedience must not be to stop the mouth of conscience, or to gain applause or preferment; but that we may grow more like God, and bring more glory to him.” That would have been the case with Adam before the fall and that should be the case now for believers. Adam had the moral law as an image bearer to glorify God. Restored sinners have been placed in a similar position to do the same. To be “converted” and not changed enough to live in obedience to God’s moral law would be a monstrosity.
 James T. Dennison and Jr, Reformed Confessions of the 16th and 17th Centuries in English Translation: 1552-1566, trans. Jr. James T. Dennison, vol. 2 (Grand Rapids: Reformation Heritage Books, 2010), 831-832.
 The approach that determines whether something is good or bad by examining the acts, rule, duties, etc. the person attempted to fulfill. Therefore, it could still be a “good” act even if it had bad consequences. (Christianity is a “form” of deontology.) Cf. See “deontology” in Paul Edwards, ed., The Encyclopedia of Philosophy, 8 vols. (New York: Macmillan Publishing Co., 1967) and Dagobert D. Runes, The Dictionary of Philosophy (New York: Philosophical Library, 1942).
 Cf. Michael Martin, Atheism: A Philosophical Justification (Philadelphia: Temple University Press, 1990), 13. Atheists believe they have plausible theories for moral actions. Martin says that atheists have offered “several impressive attempts” — and therefore, he says, theists cannot argue that atheism will lead to moral relativism.
 John Murray, The Epistle to the Romans, vol. 1, The New International Commentary on the Old and New Testament (Grand Rapids, MI; Cambridge, U.K.: Wm. B. Eerdmans Publishing Co., 1968), 75.
 G. I. Williamson, The Westminster Confession of Faith: For Study Classes, 2nd ed. (Phillipsburg: P & R Publishing, 2004), 179.
 Wilhemus à Brakel, The Christian’s Reasonable Service, trans. Bartel Elshout, 4 vols. (Ligonier, PA: Soli Deo Gloria Publications, 1992-95), 3:42.
 John Murray, Principles of Conduct (Grand Rapids: Eerdmans, 1957), 28-29.
 Thomas Watson, The Ten Commandments (London: The Banner of Truth Trust, 1970), 3.
 The very idea of the “moral law” is carefully developed in the subsequent LC questions.