The content of the law does not change once we are justified through faith. Rather, it is our relationship to the law which changes. Before we were Christ’s, the law stood in judgment upon us, condemning us because we cannot keep it. The law inflicts its curse upon us. But once we trust in Christ as proclaimed in the gospel, we have died to the law and its curse, and suddenly we come alive to the commandments of God, which now reveal to us the will of God, and what we may do to please him (Psalm 1:1-2). This is why the old theologians were correct when they affirmed that the law is both the teacher of sin, and the rule of gratitude.
Often identified as a Lutheran distinctive, the law-gospel distinction is recognized by the Reformed tradition as well. Reformed theologians such as Zacharius Ursinus (the principle author of the Heidelberg Catechism) and Louis Berkhof (a distinguished Reformed theologian) have spoken of the Bible as containing two parts–the law and the gospel. Although people often assume that this means the Bible has two testaments (the Old Testament being identified with “law” while the New Testament is identified with “gospel”), this is mistaken. In making the law-gospel distinction, we mean that law and gospel are two distinct but intimately connected “words” from God found throughout both testaments.
A definition or two is helpful at this point. The law is that which God demands of us (Genesis 2:17; Exodus 20:1-18), while the gospel is the good news that in Jesus Christ, God freely and graciously gives to us everything which he demands of us under the law (Romans 5:9; 2 Corinthians 5:17-21). The content of the law is that which God revealed first to Adam in Eden, and then published in the covenant God made with Israel at Mount Sinai when the Ten Commandments were written down on two tablets of stone and given to the people of God (Exodus 24).
The gospel is the message of what God has done in Jesus Christ to save us from our sins. It is good news which is declared to us from the Word of God. The revelation of this gospel begins in Genesis 3:15 when God promises to rescue Adam from the curse pronounced upon him after he rebelled against his creator and brought our race under condemnation. God promised to crush Satan under the heel of a redeemer, and ensures Adam that one day no longer will there be any curse (Revelation 22:3). The law is what God commands of us. The gospel is what God has done for us in Jesus Christ. The law says “do.” The gospel announces to us what has been “done.”
The importance of this distinction becomes clear when we survey the course of biblical history. When God created Adam and placed him in Eden, Adam was created in a covenant relationship with God (the so-called covenant of works). Adam had the natural ability to obey all of God’s commands, which are written upon the hearts of all of Adam’s descendants because we are divine image bearers (Romans 2:12-16). These commandments are not published until God gives them to Israel at Mount Sinai. In the contents of the Sinaitic covenant, we see that both law and gospel are found together in the Old Testament.