Jesus Is Not Just David's Son, He Is David's Lord (22:41-46).
Just as the Sermon on the Mount was preceded by a revelation of the glorious light that had burst on the world in Jesus (Matthew 4:16) so that the Kingly Rule of Heaven was seen to be at hand (Matthew 4:17; Matthew 4:23), so now this revelation concerning love for God and for our neighbour is followed by the revelation of the glory of the Christ, Who is to sit on God's right hand with all His enemies submitting at His feet (compare Matthew 28:18; Matthew 26:64). All that has gone between has explained why this is.
Analysis.
a Now while the Pharisees were gathered together, Jesus asked them a question, saying (Matthew 22:41).
b “What do you think of the Messiah (Christ)? Whose son is he?” They say to him, “The son of David” (Matthew 22:42).
c He says to them, “How then does David in the Spirit call him Lord, saying, “The Lord said to my Lord, You sit on my right hand, until I put your enemies underneath your feet?” (Matthew 22:43-44).
b “If David then calls him Lord, how is he his son?” (Matthew 22:45).
a And no one was able to answer him a word, neither dared any man from that day forth to ask him any more questions (Matthew 22:46).
Note that in ‘a' Jesus asks the Pharisees a question and in the parallel no one is able to answer Him or dares to ask Him an more questions. In ‘b' Jesus asks them if the Messiah is David's son, and in the parallel demonstrates that he cannot be because David calls him ‘Lord'. Centrally in ‘c' we have the evidence as to why the Messiah is David's Lord.