After facing several questions from his critics and answering them perfectly, Jesus finally decided to go on the offensive and ask them something. Understanding this passage requires a bit of background knowledge, and then we’ll try to apply it.
There were a lot of different interpretations of what the Messiah (or Christ) would be: Some thought he'd be a great political leader and help Israel rise up against the Romans, while others saw him as mostly a great teacher. Others visualized him as a prophet, since Moses predicted a successor who'd equal or surpass him. But the idea of God coming in human flesh would've been completely foreign to them.
But there was one thing that most everyone agreed upon: The Messiah would be the “son” (descendant) of David. There were a lot of kings in David’s line, but most of them didn’t even come close to David’s glory, and most of them were quite a disappointment.
Jesus didn’t dispute their answer to his question--in other words, they were correct in assuming the Messiah would be a "son" (descendant) of David--but he wanted to expand their understanding of who and what the Messiah would be. He pointed them to Psalm 110, which is actually the most quoted Psalm in the New Testament. Another thing that most religious scholars agreed upon was that it was a Messianic Psalm, predicting his arrival.
So here was Jesus’ simple question: If David (under the inspiration of the Holy Spirit) was talking about the Messiah, why would he call his descendant “Lord”? Respect was always given to your ancestors, not your descendants.
We know the answer because God’s revealed it to us through the rest of his word. The Messiah was more than merely a human teacher. He was more than a mere military leader. In fact, he was not merely human at all. In the Psalm we see a hint of the fact that the Messiah would be God-in-human-flesh and thus entitled to the title “Lord” by his ancestor: "The Lord [referring to the Father] said to my Lord [referring to Jesus]. . . "
So let’s try to apply this. Jesus’ question at the beginning is really important: “What do you think about the Christ?” Is he just a good source of advice, which is how most of the world approaches him? Or is he God-with-us, our Divine Savior and Lord?
If he is your Lord, if he is God, then that means you have some obligations to him. He deserves your ultimate loyalty, your wholehearted obedience, and your sacrificial love.
If you’ve accepted this, then have you completely trusted him with your future? The verse from Psalm 110 quotes the Father as saying “Sit at my right hand until I put your enemies under your feet.” This is the final fate of all Jesus’ enemies, from Satan on down. This Lord over the universe is also our dearest Friend, and he desires for us to trust him everything we have. Do you?
Lord Jesus, yes I trust you. Not nearly enough. I believe, Lord. Please help my unbelief.