The Messiah, the anointed One, was the promised Son of David, come to redeem the world.  But, according to Jesus, He was more than the Son of David, He was the Lord of David.  This is one of the great arguments for the incarnation being a perfect blending of the human and divine natures.  The One who went to the cross for all humanity was fully human as the Son of David, but Son of God through the Virgin Mary’s womb. David’s Son Is David’s Lord.

“And as Jesus taught in the temple, he said, ‘How can the scribes say that the Christ is the son of David?  David himself, in the Holy Spirit, declared, ‘The Lord said to my Lord, Sit at my right hand, until I put your enemies under your feet.   David himself calls him Lord. So how is he his son?’” Mark 12:35-37a (ESV)