Shorter Catechism Q. 42. What is the sum of the ten commandments? A. The sum of the ten commandments is to love the Lord our God with all our heart, with all our soul, with all our strength, and with all our mind; and our neighbor as ourselves.
Commentary: Several years ago, Tina Turner asked in a pop song, “What’s love got to do with it?” Well, as it turns out, quite a lot. Besides being the mark of a Christian (John 13:35), and the greatest virtue, even above faith and hope (1 Cor. 13:13), it is, as the Catechism teaches, the sum of the Ten Commandments. In Romans 13, Paul says that the commandments of the decalogue (he lists 4 of the 10), and “any other commandment, are summed up in this word: ‘You shall love your neighbor as yourself.” Since the Ten Commandments are a summary of the moral law (WSC 41), it follows that the same is true for the command to love. The most basic principle, therefore, of the moral law, and indeed of the entire Old Testament, is love: love for God and love for neighbor (Matt. 22:37-40).
We are to love God “with all our heart, with all our soul, with all our strength, and with all our mind.” This means that we are to love God completely and supremely. We don’t love God with half a heart, but with all our heart. We don’t love God with one part of our being (e.g. just our mind), but with every part.
We are to love our neighbor “as ourselves.” Our neighbor is our fellow human being. And we love them in the same way we love ourselves. We look out for their interests even as we look out for our own. Whatever we wish that others do to us, we also do to them “for this is the Law and the Prophets (Matt. 7:12).