Matthew 22:42

“What do you think of the Messiah (Christ)? Whose son is he?” They say to him, “The son of David.” '

First He asked them what their view was about the Messiah. Whose son did they see him to be? In the light of the beliefs of the time that was not a difficult one and they promptly replied, ‘the son of David'. David was the glorious king of the past who had overshadowed all other kings. In their eyes he was the prototype of all that was good in kingship. And to see the Messiah as his son was to see Him as glorious indeed from an earthly point of view. But Jesus' point here is that that is not enough.

Note that this is not strictly a use of the title ‘the Son of David' but is more a statement of fact in line with Matthew 1:1; Matthew 1:17 and is thus emphasising lineage, that is, that He is the son of David. He is the One in the line of David Who was promised as coming (compare Isaiah 9:2; Isaiah 11:1; Jeremiah 23:5; Ezekiel 34:23; Ezekiel 37:24). It has a slightly different nuance to the title ‘the Son of David' as used to refer to the One with royal healing powers (like Solomon), although the end result is the same for both connect Him with the house of David and with the Messiah.