Well, maybe the greatest Jewish rabbi of the second millennium was Rabbi Maimonides, who died near the end of the 12th century. Among other things, he is noted for recording an orderly list of 613 commandments found in Torah (first five books of the bible). These ‘commands’ range from the ‘miscellaneous’ kind (e.g., no body tattoos, no cross-dressing, etc) to the ‘sublime’ (e.g., to believe in the One Eternal God and hallow His Name).
Centuries earlier, in Jesus’ day, disputes among Pharisees about these various ‘commands’ were endless, especially when the subject was “ranking” the commands according to their supposed importance. The “rank” determined the greater or lesser severity of punishment when such a law was broken. It is into this dispute that the scribes tried to draw Jesus. Of course, they are trying to “test” or “trap” him by asking him to pick the “greatest command,” because if he chooses one law, they can accuse him of showing disrespect for all the other divine laws.
Jesus does not give in to their “trap” to debate these issues. He sees clearly that the Pharisees – supposedly experts in the law – are focusing too much on specific problems and need to have the applicable point explained to them (or, as we say today, they couldn’t see the forest for the trees). So Jesus ‘cuts to the chase’ and goes directly to the two core principles which underpin all 613 ‘commandments.’ These are: (1) love God with your whole being; and (2) love your neighbour with your whole being. Everything is based on this foundation, even the law itself.
Jesus tells them that all the Law and the Prophets must be interpreted in the light of the command to love God and neighbour. The divine commands make explicit the response we are required to give to God. The only way to remain in God’s love is to keep his commandments.
Also see articles #2055; #2083 and #1824 in the Catechism of the Catholic Church.