He relates his question to a word of scripture, Psalm 110. This psalm was recognized by the Jews as messianic a long time ago. According to the Old Testament, there is also no question that the Messiah is the son of David(Jer 23:5 etc.). So if this psalm is about the son of David, how can King David refer to his own son as Lord ? Sons may have called fathers masters, but not the other way around!
The scribes could not find an answer to this. And to this day, this question has not been answered in Judaism.
You can only answer the question if you really know the person of the Lord Jesus. He is true God and man in one person. As a man (born in lowliness) he is the son of David, and as the Son of God (as well as the glorified Lord) He is David’s Lord. The Lord Jesus described himself as the root and lineage of David (Rev 22,16). He is the origin of the tribe of Jesse and also the offspring (Isa 11:1). Lord and Son!
