Michael Horton: What the Third Use of the Law Can and Cannot Do
"We may carefully distinguish law and gospel in justification but then confuse them in our treatment of the Christian life. . ."
Having defended this third use of the law, it is equally important to remind ourselves what the law can and cannot do even according to this third use. After all, the impression can sometimes be given that while the law cannot justify us, it can sanctify us. We may carefully distinguish law and gospel in justification but then confuse them in our treatment of the Christian life, as if those who are now justified can derive strength from the law for their homeward journeys. This, however, is as impossible in sanctification as in justification. In the various uses of the law, its basic function never changes: it commands; that is its office.
". . . the law, its basic function never changes: it commands; that is its office."
The law (considered as God’s “command”) never does more than that. Whether the Decalogue or Paul’s teaching on the fruit of the Spirit, such moral instruction can guide, can tell us what our gracious Father calls us to do, but it can never animate our hearts or motivate our hands. That is why obedience is the fruit of the Spirit. Jeremiah’s prophecy, remember, is not only of forgiveness of sins but of a total restoration, beginning with regeneration and a new obedience.
"it [law] can never animate our hearts or motivate our hands."
This heartfelt trust and obedience was God’s intention all along. God created us in his image, as his own people, to reflect his glory and to rule over the rest of creation faithfully in his name until the whole earth would become full of his glory. We were created strong, not weak; faithful, not unfaithful; righteous, not wicked; God-centered, not self-centered. The fall created a break, a fissure, a departure. Nevertheless, God could not change his moral nature or the expectations he had for humanity as his image-bearers. God would not stop until he completely restored that image and was able to commune with humanity as a full partner again.
Michael Horton, God of Promise, 188.