What is the difference between obeying God under the law and obeying God under grace? The ultimate purpose of both is obedience to God, but this obedience is accomplished in different ways. To illustrate this point, let’s look at a simple commandment given in both the Old Testament, under the law of Moses, and the New Testament, in one of the epistles. The exact words are used, and they apply whether we are under the law or under grace.
In the Old Testament, God was speaking through Moses to Israel, and He said, “For I am the Lord who brings you up out of the land of Egypt, to be your God. You shall therefore be holy, for I am holy” (Leviticus 11:45). In context, “being holy” means that you have to keep a set of extremely complicated rules, which are delineated in great detail throughout the remainder of the book of Leviticus. In this case, holiness is attained by the methods of legalism: “Do this. Don’t do that.”
The New Testament passage is addressed to Christians who have accepted Jesus’ redemption on their behalf: “As obedient children, not conforming yourselves to the former lusts, as in your ignorance; but as He who called you is holy, you also be holy in all your conduct, because it is written, ‘Be holy, for I am holy’” (1 Peter 1:14–16). The quotation is taken from Leviticus, so does that mean Peter was telling us that we must observe all the Old Testament rules about animal sacrifices and mildews and bodily fluids? Obviously not. So, he must expect something different. The holiness of the law says, “I have to keep all these rules.” The alternative response of faith is, “I don’t follow a set of rules. I let Jesus be holy, in me and through me.”