The enemies of Jesus tried constantly to catch Him making a mistake or teaching error, but they never succeeded; then He started asking them questions, including this one,

Then Jesus answered and said, while He taught in the temple, “How is it that the scribes say that the Christ is the Son of David? For David himself said by the Holy Spirit:

‘The Lord said to my Lord,
“Sit at My right hand,
Till I make Your enemies Your footstool.”’

Therefore David himself calls Him ‘Lord’; how is He then his Son?” And the common people heard Him gladly (Mark 12:35–37).

His critics knew that the Messiah was David’s Lord, and they knew that the Messiah was David’s son, but they never put the two together evidently, and never tried to reconcile those teachings. The Christ (Messiah) is the Lord, but He humbled Himself and became a man, making Himself the son of David, as well as the Lord of David.