Let's look at it more closely.
In Matthew 24 we see Jesus having a conversation in which he asks the Jewish leaders (Pharisees in this case) about the Messiah that they are awaiting. Jews today are still waiting for this same Messiah, who they say MUST come from the house of David. It's the very reason Jesus asks them this question, and in doing so he quotes Psalm 110.
While the Pharisees were gathered together, Jesus asked them, Saying, What think ye of Christ? whose son is he? They say unto him, The Son of David. He saith unto them, How then doth David in spirit call him Lord, saying, The LORD said unto my Lord, Sit thou on my right hand, till I make thine enemies thy footstool? If David then call him Lord, how is he his son? And no man was able to answer him a word, neither durst any man from that day forth ask him any more questions.
I'll paraphrase--
Jesus-- The coming Messiah-- where will he come from?
Pharisees-- From the house (lineage) of David.
Jesus-- How can this be?- when David tells us that while in spirit, God said to 'the master' (the Messiah- David's master) -Sit at my right hand until I make your enemies your footstool. The point is-- if the Messiah must be David's son, why does David refer to him as his master? -something a king would not call his descendant... ever. There is no way for a son to be a King's 'lord.' (master)
The text tells us that the question left them speechless. In Jewish thought, the coming Messiah would assume David's throne because he would be of David's line, but it would always be David's throne. In no manner of speaking would the coming Messiah take supremacy over David-- so why would David ever refer to that one as 'his master'? Their unspoken answer was-- he wouldn't. But he did. And they had no explanation.
What was Jesus' actual point? The translators (including the Lockman Foundation) would have you believe that Jesus was claiming to be God. This is why they insert that capital "L" -- the text does no such thing and doesn't have Jesus making any such claim. Jesus is pointing out that David knew that the Messiah (anointed one) was not 'him' but another. One from above. One God (the Father) called (David's master).