Mark 12:35-37 (ESV)
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?" And the great throng heard him gladly.
What Jesus takes issue with here, is that the scribes conceive of the Christ too narrowly. This happens even today, when faith alone is used to nay say baptismal regeneration. Rather than looking at the whole picture people have a tendency to grab what they like and agree with and run with that interpreting it in a manner that doesn’t allow for other verses to speak. Perhaps an interpretation of Revelation that excludes the rest of the scriptures, or interprets the rest of scripture in such a way that it is at odds with itself but in agreement with a preconceived interpretation of Revelation.
Here Christ is bringing out another aspect of who the Messiah, the Christ is. He is Lord. David in psalm 110 pries into the mystery of the trinity, showing that God is one even as he is more than one, the Lord’ says to my Lord. The Lord is the Christ, David’s Son, is David’s Lord, even as Mary gave birth to her creator, her God.