God’s moral law is found on the consciences of all people, but when the Reformers discussed the right use of the law, they had in view primarily the moral law in its written form that is part of the Mosaic law in Scripture. As we have seen, this written law (and even the law on the conscience) restrains sinners, keeping them from being as bad as they could possibly be (1 Cor. 5:1; 1 Tim. 1:8–11). It also reveals our sin, pointing out our need for the righteousness of Christ in order to be justified before God (Rom. 7:7–25; Gal. 3:24). But there remains one more use of God’s law that the Protestant Reformers recognized, and for some such as John Calvin it was the most important use of the law. We are referring to the law of God as a guide to what pleases God, as direction for walking in holiness.
Many passages teach the use of the moral law as our guide. Today’s passage, for example, notes that the way to avoid sinning and displeasing God is to store the law of God in our hearts (Ps. 119:9–11). In order not to sin against the Lord, we must know what pleases and displeases Him, and the way to know such things is to be so thoroughly familiar with His law that it is part of our very being. We must know and be controlled by the law in the heart, the core of personal identity and action. Texts such as Matthew 5:17–20 also teach the necessity of the ongoing guidance of the moral law. Jesus explains that not even the smallest part of God’s law will pass away until He accomplishes and fulfills it. Since the work of Christ will not be consummated until He returns and we are resurrected in glorified bodies that will not sin (1 Cor. 15), the moral law has not yet been fully accomplished. The moral law points finally to the new creation when obeying God will be second nature, so as long as sin abides and we fall short, we must have the moral law to guide us.
Summarizing this use of the law, the Westminster Confession of Faith states, “Although true believers be not under the law, as a covenant of works, to be thereby justified, or condemned; yet is it of great use to them, as well as to others; in that, as a rule of life informing them of the will of God, and their duty” (19.6). The law of God corrects our misunderstandings of right and wrong. It helps us understand that God-pleasing good works include both the right action and motivation. It helps us discern the right way to go when we must make decisions. It is God’s good gift to equip us for pleasing Him in all that we think, do, say, love, and believe.