Reformed Doctrine Daily Devotions

⁴³  He said to them, “Then how does David in the Spirit call Him ‘Lord,’ saying,
    ⁴⁴  ‘THE LORD SAID TO MY LORD,
         “SIT AT MY RIGHT HAND,
         UNTIL I PUT YOUR ENEMIES BENEATH YOUR FEET”‘?

 ⁴⁵  “If David then calls Him ‘Lord,’ how is He his son?”

 ⁴⁶  No one was able to answer Him a word, nor did anyone dare from that day on to ask Him another question.

Calvin in his Commentary states in part:

“… Now as the hour of his death was already approaching, the Lord himself intended to attest his divinity, that all the godly might boldly rely on him;  for if he had been only man, we would have had no right either to glory in him, or to expect salvation from him.  …

Yet it must be observed, that the scribes are not reproved for teaching that Christ would be the Son of David, but for imagining that he was a mere man, who would come from heaven, to assume the nature and person of a man.  … 

We must now see how he proves that Christ will hold a higher rank than to be merely descended from the seed of David. It is because David, who was king and head of the people, calls him Lord; from which it follows, that there is something in him greater than man. …

In short, by this title Christ is pronounced to be supreme and sole King, who holds the preeminence among all believers; and no exception ought to be allowed to ranking all in one class, when he is appointed to be the Redeemer of the Church.  …

The Lord said to my Lord.  Here the Holy Spirit puts into the mouth of all the godly a song of triumph, that they may boldly defy Satan and all the ungodly, and mock at their rage, when they endeavor to drive Christ from his throne. …

Whenever this kingdom is violently attacked, let us call to remembrance this revelation from heaven; for undoubtedly this promise was put into the hand of Christ, that every believer may apply it to his own use. …

And God declares that Christ will sit till his enemies be subdued, in order to inform us that his kingdom will remain invincible against every attack; not that, when his enemies have been subdued, he will be deprived of the power which had been granted to him, but that, while the whole multitude of his enemies shall be laid low, his power will remain for ever unimpaired.  In the meantime, it points out that condition of his kingdom which we perceive in the present day, that we may not be uneasy when we see it attacked on all sides.”