What does Luke 20 verse 44 mean?

Luke 20 41And he said unto them, How say they that Christ is David's son? 42And David himself saith in the book of Psalms, [Jesus here quoted Psalm 110] The LORD said unto my Lord, Sit thou on my right hand, 43 Till I make thine enemies thy footstool. 44 David therefore calleth him Lord, how is he then his son? In talking to the scribes of the Sadducee sect, Jesus asked the rhetorical question, "How say they that Christ is David's son?" He then asked, "David therefore calleth him Lord, how is he then his son [ descendant]?

In the context of the previous section, where the Sadducees were trying to trap Jesus with a question they thought he could not answer, He then asked them a difficult question, which they could not answer without understanding The Bible. Christ is paradoxically, a descendant of King David ( his 'son'), and His Lord, the Messiah. The Saduccees did not understand that.

It was at the time commonly believed that in "the LORD said unto my Lord" "my Lord" referred to the expected Messiah. The Messiah was to be a descendant of David, as well as his God.