Shorter Catechism Q. 41. Where is the moral law summarily comprehended? A. The moral law is summarily comprehended in the ten commandments.
Commentary: The Catechism teaches that the Ten Commandments are moral law. Although there are some ceremonial or typological aspects within it (e.g., the promise of long life in the land), they are substantially moral law. Moral laws are commands that are universal (applies to all persons) and perpetual (applies at all times), which is what the Ten Commandments are. They are general, unconditional imperatives (“You shall not…You shall…”), which address fundamental issues that pertain to all human beings in every age: worship, use of time, family, violence, sex, property, speech and desire.
The Catechism also teaches that the Ten Commandments are a summary of the moral law. They are a brief condensation of what God requires of us. Jesus teaches the summary nature of the Ten Commandments in the Sermon on the Mount. He says that the command, “You shall not murder,” doesn’t merely prohibit the act of murder, but that it also forbids sinful anger and sinful speech. This indicates that the sixth command is a summary statement of God’s law pertaining to the preservation and treatment of human life.
Since the Ten Commandments are only a summary of God’s moral law, they do not tell us everything we need to know about it. A summary, by its very nature, is not comprehensive. It needs to be unpacked and explained. For example, it is not enough to know that we are to honor our parents. We need to know what that means, and how it applies to young children and to adult children. This is why the Catechism will go on to expound the Ten Commandments in questions 45-81.