There are three wonderful uses of the Law in the lives of believers (and society at large):

First, the Law Drives Sinners to Christ for Grace. As the Law reveals the holiness of God and the sinfulness of sinners, when a person is convicted by the Holy Spirit of his sinfulness before a holy God and is regenerated by the Holy Spirit, he will flee to Christ for grace. This is why the Law must be preached evangelistically. No one will run to Christ for grace if he does not first understand that, before a holy God, he is sinful, headed for judgment, and worthy of wrath [1].

Second, the Law Restrains Evil. Because the Law has no power to change sinful hearts, some might argue that it has no power to restrain evil in society. Although the Law and its threat of punishment for wrongdoing might not be the most noble reason to refrain from doing evil, the fear of punishment does keep some individuals from doing what they might otherwise do if it were not for the Law. This is called God’s “restraining grace.”

Third, the Law Reveals God’s Holiness. Paul states this point clearly in Romans 7:12. The Law reveals God’s standards of holiness for mankind. Even if a person could obey God’s Law perfectly, it would not make him sinless or innocent before God, since people not only commit sin but are born with a sinful nature (original sin). In the lives of Christians, however, the Law reveals the principles of holiness by which believers are to live—not to earn salvation, but out of gratitude for having been saved by God’s grace alone, received through faith alone, in Christ alone, for the glory of God alone!

Footnote:
[1] One of the key reasons people do not understand the sinfulness of sin is that they do not understand the holiness of God. Knowing God’s holiness instantly makes one aware of sin. (See Isaiah 6:1-5.)