Jesus’ answer to the question regarding the most important commandment goes beyond what He was first asked. After explaining that wholehearted love for God is the most important rule, He identifies the second greatest commandment — we must love our neighbors as ourselves (Mark 12:28–34). On both commandments “depend all the Law and the Prophets” (Matt. 22:34–40); thus, the Heidelberg Catechism uses love for God and neighbor to summarize the Lord’s requirements (Q&A 4).
Of course, in describing love of neighbor as the second most important commandment, our Savior is not thereby telling us to be less concerned with loving our neighbor than we are with loving the Lord; rather, Jesus gives us the logical priority of these two commandments. Obviously, love for God must come first because if we do not love God then we do not care about His commandments (John 14:15), and if we do not care about His commandments, we cannot learn how to love our neighbors. In terms of logical precedence, love for the Lord comes first, but, practically speaking, the two commandments are inseparable. Christ, through the Apostle John, later explains that we do not love God if we do not love others, especially fellow Christians (1 John 3:10; 4:20–21; 5:1). True love for the Lord always manifests itself in love for one’s neighbor.
God’s command for His people to love their neighbors is not an entirely new thing for the new covenant church but a law that was also given to old covenant Israel (Lev. 19:18). And like the command to love the Lord wholeheartedly, the command to love one’s neighbor is also unfolded for specific situations through the other laws God has given us, particularly the prohibitions against disrespecting parents, murder, adultery, theft, slander, and coveting (Ex. 20:12–17). Moreover, obeying the command to love our neighbors involves both outward conformity to God’s regulations and proper heart attitudes toward others. As Matthew Henry explains, “We must be badtempered towards none,” and “we must be good-tempered to all.”
At the end of the day, however, the summary command to love our neighbors as ourselves, just like the greatest commandment, exposes our sin and misery. We are a selfish people who are inclined to put ourselves first and not care about the good of others. If it were otherwise, Scripture would never have to command us to love others.