What does Mark 12:37 mean?

Just as the spiritual priesthood of Melchizedek supersedes that of Abraham's descendants (Hebrews 7), David understands that God's spiritual kingdom has supremacy over Israel. This is what Jesus has been trying to teach the disciples for the last three years. He has not come to rescue Israel from foreign threat—yet (Jeremiah 30). First, He must fight the spiritual battle for the souls of humanity.

It's unclear how much the crowds fully understand. Jesus has been debating the Jewish religious and civil leaders all day, by turns frustrating and impressing them with His wisdom. The Pharisees understand that many consider Jesus to be the Messiah but, like the disciples, do not understand who the Messiah really is and what He has come to do. Many think He has just come to free Israel from Roman rule, a thought which terrifies the Herodians and Sadducees who stand to lose their influence and authority. The Pharisees and scribes understand from their many altercations that if Jesus comes to ruling position, He will eradicate the manmade traditions by which they lord over the people.

In this last week, Jesus obliquely poked at the religious teachers in a way that left no doubt that He was claiming to be God and the Son of God. Here, He uses David's own prophecy to show that the Messiah, David's "son," has authority over David, himself. The Messiah isn't just the earthly son of a king, come to reestablish that kingdom.

The text is unclear as to why Jesus adds this teaching, but the crowd's reaction hints at a possibility. Jesus has challenged the authority the Herodians and Pharisees (Mark 12:13), the Sadducees (Mark 12:18), and the scribes (Mark 12:28). Now, the religious leaders have nothing to say (Mark 12:34; Matthew 22:46). The people, however, are delighted by the show, and ready to hear a more thorough condemnation of the scribes and Pharisees (Matthew 23).