From The Gospel of Matthew, by Curtis Mitch and Edward Sri, commenting on Matthew 22:34-40
Polemics continue as the Pharisees return with another challenge for Jesus. This time they send a scholar of the Mosaic law. The question is a simple one: Teacher, which commandment in the law is the greatest?
This is not a trick question but is designed to see if the Galilean preacher has the knowledge necessary to be teaching others about God and his will for their lives. Jesus replies by citing the love commandments from Deut 6:5 and Lev 19:18.
The first is part of the Shema, the monotheistic creed of Israel that the faithful recited as part of their daily prayers. It is the greatest commandment of the Torah because it spells out the highest obligation of every person, which is to love the Lord with the combined strength of one’s heart, soul, and mind. The love he demands is not simply affection or emotion but a commitment to keep the Lord’s covenant.
The second commandment calls us to love our neighbor with the same solicitude with which we naturally care for our own needs. Earlier Jesus applied this precept to friends and enemies alike (5:43–48), declaring it one of the requirements for gaining eternal life (19:19). Together the two love commandments sum up the Ten Commandments, three of which delineate our responsibilities toward God and seven of which concern our duties toward others (see Exod 20:2–17).
To stress the point, Jesus adds that the whole law and the prophets depend on these two commandments. Literally, the text says that the Torah and the Prophets “hang” on the double love commandment, as though these two precepts support the full weight of biblical religion in all its various aspects. No other commandment of the Bible is properly observed if either one of these is transgressed or compromised, for the aim of all divine Scripture is to bring us out of ourselves to love and serve God and our fellow human beings.