@Studyman
The question arises among Christians as to how the Old Testament Law applies to the life of them. Is it done away with completely, are we bound to it completely, or are we bound to portions of it?
Christianity at the time of the Reformation brought the apostolic teaching back to salvation by grace through faith alone, not on obedience to the Old Testament law for salvation. Yet the law of God was not repudiated. It was Calvin who wrote in his Institutes what is known as the threefold purpose of the law. (Note: just because Calvin said it that does not make it false, even if one despises. Some need to put things in their proper place through use of common sense.) He did this in order to show the importance of the law for the Christian life.
The first purpose: to be a mirror. His law reflects and mirrors the perfect righteousness of God. It tells us much about who God is. Perhaps even more importantly it shines a bright light on human sinfulness. Augustine wrote "The law orders that we, after attempting to do what is ordered, and so feeling our weakness under the law, may learn to implore the help of grace." So the law highlights our weakness so that we seek the strength found in Christ alone. The law is a severe schoolmaster that drives us to Christ.
The second purpose of the law was for the restraint of evil. The law cannot change human hearts in and of itself. However it can protect the righteous from the unjust. So the law allows for a limited measure of justice on the earth until the final judgment.
The third purpose of the law is to reveal what is pleasing to God. It enlightens the believer, the children of God, as to what is pleasing to our Father whom we seek to serve. This is the highest function of the law. It is an instrument for the people of God to give HIm glory and honor.
Meditating on the law of God is our school of righteousness. This moral law of God is always binding on us. Our redemption is from the curse of God's law, not from our duty to obey it. Our justification is not from obedience to the law, but that we might become obedient to it. To love Christ is to love His commandments. To obey God is to obey His law.
The New Testament makes clear that in the new covenant, the covenant of grace and through faith in Christ, we are not bound under the ceremonial laws of the old covenant, but to His moral law---the law of His character that His children are to reflect as His image bearers. The ceremonial laws were for reminding the Israelites of who He is and what He had done for them, and were pointing to Christ as the substitute for sins.