Matthew has written Mark’s story (Mk 12, 28-34) and made what was a scholastic dialogue in to a controversy. Unlike in Mark where the scribe is friendly, here the “lawyer” (the only occurrence of “nomikos” = lawyer in Matthew) is hostile, and the question is asked to “test” Jesus (only the devil and the Pharisees are the subject of the verb, “test”). The lawyer addresses Jesus as “Teacher”, which is an indication of insincerity, because in Matthew, believers address Jesus as “Lord”. The rabbis counted 613 commands (248 positive and 365 negative), and some regarded all commandments as equal. The question of the lawyer may have been intended to draw Jesus into a debate and get him to make a statement that could be interpreted as disparaging toward the Law.
In his answer, however, Jesus brings together two Old Testament texts that existed separately and in different books of the Bible. The commandment to love God alone was found in Deut 6, 4-5 and the commandment to love neighbour was found in Lev 19,18. These two, Jesus brings together into one, making them dependent on each other. This combination is distinctive of the Synoptic Jesus.
In his first letter John makes a telling point when he says that the one who says that he/she loves God whom they cannot see but cannot love their brother/sister whom they can see are liars (1 John 4,20).