In Reformed theology, the law has been seen as the guide for believers in the conduct of their lives. John Calvin described this as its principal use. In this sense, we are talking about the Decalogue — the Ten Commandments — and its entailments, not the ceremonial or the civil law, nor the law in its old covenantal terms.
This does not mean that the law has any inherent power to change us. Paul establishes this point in Romans 7:1–8:8. The law is weak, not because of any defect in itself but due to our sinful natures. It exposes our sin but leaves us there; indeed, it exacerbates our sinful inclinations, not by its intent but incidentally, due to the wickedness of our hearts. Only the Holy Spirit can give us new hearts and enable us, in union with Christ, to obey God.
The third use of the law asserts that the law is our rule of life as Christian believers. This is because it is based on creation ordinances: the worship of God, work and rest, marriage and the family. As such, it is rooted in the law of nature impressed on man’s heart at creation, and so it is applicable to all people at all times.
The law exposes what sin is and so warns us to avoid it. Simultaneously and conversely, its negations express positive requirements and point us to what is pleasing to God. The first four commandments relate to the worship of the one living God, in the image He has chosen (Jesus Christ), in sincerity, faith and awe, and on His appointed day. The rest of the commandments require appropriate respect for those in God-given authority, the preservation of life, marriage, property, and personal reputations, besides contentment with God’s gracious provisions. These are expressions of love — love towards God our Creator and Redeemer, and love towards people in supporting and developing their well-being.
As such, the law expresses the unchanging will of God for His creatures and is no more open to change than God Himself. Not only does the Decalogue express God’s will for man in creation, it continues to the end of the age. The promise of the new covenant given through Jeremiah affirms that in it God will write His laws on our hearts (Jer. 31:31–33).
Jesus reaffirms and intensifies the law in the Sermon on the Mount against rabbinic externalization. He applies it consistently not only to actions but to thoughts, words, and personal attitudes. He severely warns any who claim that it is abrogated (Matt. 5:17– 20). His reduction of the Mosaic law to two great commandments (Matt. 22:34– 40) is not an announcement that the Decalogue has been replaced; instead, “Matthew probably interpreted the double commandment to love as a summary of the Decalogue” (W.D. Davies and Dale C. Allison, Jr., The Gospel According to Saint Matthew, 3:245), for the rest of the commandments depend on them (R.T. France, The Gospel According to Matthew, pp. 318–320). Jesus is summarizing the whole law in a couple of comprehensive statements, placing it in the context of love. Obedience to the law in the true sense is indicative of love for God and other people. The law describes how the grace of love is to be exercised.
Other New Testament writers also reiterate the Ten Commandments and apply them to their contexts. Paul affirms that the law is spiritual — holy, just, and good (Rom. 7:12). However, by nature we are sinful and weak, and cannot keep it. Notwithstanding, the Holy Spirit changes us and enables us to fulfill its righteous requirements (Rom. 8:1–4). James uses it to stress the details of Christian living in no uncertain terms. Every one of the commandments is of vital significance (James 2:8–12). The author of Hebrews indicates that the Sabbath commandment remains, pointing us to the future eternal rest we will share with God in Christ, entering the rest He enjoyed at creation (Heb. 3:7–4:11). Since the Sabbath explicitly looks back to creation (Ex. 20:8–11), it is far more extensive in its scope than Israel alone and so anticipates the consummation of the new creation in which the redeemed will share God’s delight in His transcendent and finished work.
This has been the consistent teaching of the Christian church throughout its history. It is not a prerogative of a certain branch of Reformed theology. Despite popular misconceptions, Martin Luther taught that while believers were no longer under the law, they continue to need the preaching of the law. Philip Melanchthon took this further and the Formula of Concord (1576) expressed the law’s necessity for believers insofar as they are still fleshly. Similarly, the Thirty-Nine Articles of the Church of England (1563, 1572) states that “no Christian man whatsoever is free from the obedience of the commandments, which are called moral.” Rome argues similarly, both in its recent catechism and earlier at the Council of Trent, referring back to Augustine as an authority. Indeed, “from the start the church assigned the Decalogue a special place in catechesis, as a privileged and universally valid expression of the divine will” (Sofia Cavalletti, in Encyclopedia of the Early Church, Oxford University Press, 1992, 1:222). At various times, antinomian groups have arisen to trumpet the claim that Christ ended the law. This would strike at the heart of the gospel, for the atonement and our justification are based on the continuing validity of the moral law, which Christ obeyed, leaving us an example that we should follow in His steps.
The first commandment requires worship to be directed only to Yahweh, the God and Father of our Lord Jesus Christ. All other foci that dominate us are forms of idolatry.
The second commandment, in forbidding worship through man-made images, directs us to worship God in the image He has presented, Jesus Christ His Son, one with the Father from eternity.
The third commandment prohibits taking the name of the Lord our God in an empty manner. It directs us to sincerity, faith, and reverent awe in addressing Him.
The fourth commandment requires us to observe God’s own patterns of work and rest. He labored in creating the universe and then rested, delighting in all He had done. Now that Christ has come, we also look forward to the resurrection of the dead and the life of the world to come, in the consummated new creation. We do so on the first day of the week with the covenanted people of God.
The fifth commandment requires age-appropriate respect for our parents. God has ordained that authority be exercised on His behalf by humans, and we are to give the intelligent respect due to the family and to other organs of legitimate rule. There is a promise attached to this command; the implication is that settled order is a good provided by God.
The sixth commandment points to the sanctity of human life, which is not to be taken outside of righteous, public contexts such as just wars and as punishment for capital offenses. It directs us to do all we can to preserve and enhance human life.
The seventh commandment defends the creation ordinance of marriage between a man and a woman. This is intended by God for the good of the human race. Adultery, fornication, and homosexuality are all attacks on marriage. The commandment directs us to maintain and enhance marriage in every way possible.
The eighth commandment safeguards private property. God is the owner of all creation and has entrusted small segments of it to humans as stewards. It declares that not only is the seizure of what belongs to another offensive in God’s sight but also that the expropriation of property by private, public, or other corporate institutions or by one country over another is sin.
The ninth commandment is intended to protect personal reputations. It warns against false witness against another in a court of law. It requires us to do all we can to maintain the good name of other people.
The tenth commandment explicitly applies to our inward attitudes. It warns against greed and a desire to possess what rightfully belongs to someone else. It urges upon us the grace of contentment with the circumstances in which we have been placed.
By giving us His law, God has set us free from bondage to the opinions of men; it is a charter for Christian liberty. That is why the Westminster Confession’s chapter on the law of God is followed directly by one on Christian liberty — bound in conscience to God’s law, we are free from the dictates of men when they conflict with it or seek to usurp it (WCF 19–20).
In short, the law defines for us what is pleasing to God and what is sin. It is a map, explaining to us how our sanctification is to take shape. The Spirit uses it for that purpose. We neglect it to our eternal peril.