"...the Pharisees being gathered together, Jesus asked them, saying: 'What think you of Christ, whose son is He?' They say to Him: 'David's.' He saith to them: 'How then doth David , in spirit, call Him Lord, saying: The Lord saith to My Lord: Sit on my right hand until I make Thine enemies Thy footstool?' If David then call Him Lord, how is He his son? And no man was able to answer Him a word; neither durst any man, from that day forth, ask Him any more questions." (Gospel for the Seventeenth Sunday after Pentecost, St. Matthew xxii)
"The Lord said unto my Lord, Sit on My right hand, until I make Your enemies Your footstool" We ought, therefore, thoroughly to consider this question proposed to the Jews by the Lord ... . For if what the Jews answered be asked of us, whether we confess or deny it; God forbid that we should deny it. If it be said to us, 'Is Christ the Son of David, or not?'; If we reply, 'No', we contradict the Gospel ... . ...
The Jews, then, when questioned by Christ, whose Son they believed Christ to be, rightly answered, the Son of David. The Gospel agrees with their answer. Not only the suspicion of the Jews, but the faith of Christians, does declare this.... 'If then David in the spirit called Him Lord, how is He his son?' The Jews were silent at this question: they found no further reply: yet they did not seek Him as the Lord, for they did not acknowledge Him to be Himself that Son of David.
But let us, brethren, both believe and declare: for, 'with the heart we believe unto righteousness: but with the mouth confession is made unto salvation'; let us believe, I say, and let us declare both the Son ofDavid, and the Lord of David. Let us not be ashamed of the Son of David, lest we find the Lord of David angry with us.
...We know that Christ sits at the right hand of the Father, since His resurrection from the dead, and ascent into heaven. It is already done: we saw not it, but we have believed it: we have read it in the Scripture, have heard it preached, and hold it by faith. So that by the very circumstance that Christ was David's Son, He became His Lord also. For That which was born of the seed of David was so honored, that It was also the Lord of David.
You wonder at this, as if the same did not happen in human affairs. For if it should happen, that the son of any private person be made a king, will he not be his father's lord? What is yet more wonderful may happen, not only that the son of a private person, by being made a king, may become his father's lord; but that the son of a layman, by being made a Bishop, may become his father's father. So that in this very circumstance, that Christ took upon Him the flesh, that He died in the flesh, that He rose again in the same flesh, that in the same He ascended into Heaven, and sits on the right hand of His Father, in this same flesh so honored, so brightened, so changed into a heavenly garb, He is both David's Son, and David's Lord....
Christ, therefore, sits at the right hand of God, the Son is on the right hand of the Father, hidden from us. Let us believe. Two things are here said: that God said, 'Sit on My right hand;' and added, 'until I make Your enemies Your footstool;' that is, beneath Your feet.
'Thou dost not see Christ sitting at the right hand of the Father: yet you can see this, how His enemies are made His footstool.' While the latter is fulfilled openly, believe the former to be fulfilled secretly. What enemies are made His footstool? Those to whom imagining vain things it is said, 'Why do the heathen so furiously rage together: and why do the people imagine a vain thing?'.. ..He therefore sits at the right hand of God, till His enemies be placed beneath His feet. This is going on, this is taking place: although it is accomplished by degrees, it is going on without end. [Hoc fit, hoc agitur: etsi paulatim peragitur, indesinenter agitur.]
Enarrationes in Psalmos (In Psalmum CIX)