What does Mark 12:29 mean?

A scribe has asked Jesus what the "most important" or foundational commandment is (Mark 12:28). The Mosaic law has 613 commands, and the scribes added many others in the Oral Law. While all the written laws are to be obeyed, they each have a certain priority in the minds of the religious leaders. Jesus' response is: know God, love God (Mark 12:30), love others (Mark 12:31). These commandments cover all of God's requirements (Romans 13:8).

In this verse and Mark 12:30, Jesus quotes Deuteronomy 6:4–5 which is the beginning of the Shema prayer. Shema is from the Hebrew word for "hear," which is the first word of the saying. Devout Jews pray the Shema in the morning and night as a way of fulfilling Deuteronomy 6:7: "…talk of [the laws]…when you lie down, and when you rise."

Jesus only quotes the part about loving God. The prayer continues by convicting the people to remember the Law and teach it to their children (Deuteronomy 6:4–9). The full traditional prayer adds that God will bless their obedience (Deuteronomy 11:13–29) and that the Jews need to sew tassels for their cloaks as reminders to follow the Law (Numbers 15:37–41).

After quoting that we are to love God, Jesus continues that we are to love others (Mark 12:31). But it's interesting to note that the "greatest commandment" doesn't start with loving God and others, but with "hear." The first principle we need to obey is to hear and understand and accept that the Lord is our God and the Lord is one. The rest of the Mosaic law—in fact, all of Scripture—means nothing without the understanding of who God is.