See what Calvin says about the moral law in his "Institutes", particularly it's three fold use. See what the WCF and Larger Catechism says about the law and it's threefold division, moral, ceremonial, judicial. If you can get a hold of "The Revelation of Law in Scripture" by Patrick Fairbairn, that'd be good. Fairbairn is one of the great Reformed biblical theologians. His book may be online? Also "Principles of Conduct" by John Murray discusses the role of the law in a believer's life among other things. Any of the standard works on the Ten Commandments are good e.g. Thomas Watson, Jochem Douma. etc. Avoid the theonomists/Christian reconstructionists until you have studied books such as the above. They have an idiosyncratic view of the judicial law that is not in the mainstream tradition of the Reformed faith and does not agree with the Confession.
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