From http://www.gotquestions.org/Christian-law.html
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In place of the Old Testament law, Christians are under the law of Christ (Galatians 6:2), which is to “love the Lord your God with all your heart and with all your soul and with all your mind…and to love your neighbor as yourself” (Matthew 22:37-39). If we obey those two commands, we will be fulfilling all that Christ requires of us: “All the Law and the Prophets hang on these two commandments” (Matthew 22:40). Now, this does not mean the Old Testament law is irrelevant today. Many of the commands in the Old Testament law fall into the categories of “loving God” and “loving your neighbor.” The Old Testament law can be a good guidepost for knowing how to love God and knowing what goes into loving your neighbor.
“This is love for God: to obey his commands. And his commands are not burdensome” (1 John 5:3). The Ten Commandments were essentially a summary of the entire Old Testament law. Nine of the Ten Commandments are clearly repeated in the New Testament (all except the command to observe the Sabbath day). Obviously, if we are loving God, we will not be worshipping false gods or bowing down before idols. If we are loving our neighbors, we will not be murdering them, lying to them, committing adultery against them, or coveting what belongs to them. The purpose of the Old Testament law is to convict people of our inability to keep the law and point us to our need for Jesus Christ as Savior (Romans 7:7-9; Galatians 3:24).
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Good answer.