John Gill Commentary Luke 20:42

"For David himself saith in the book of Psalms, The Lord said unto my Lord, Sit thou on my right hand," — Luke 20:42 (ASV)

And David himself says in the book Psalms In (Psalms 110:1) the Lord said to my Lord, sit you on my right hand ;

which words were delivered by David, as inspired by the Spirit of God; and contain a speech of God the Father to his son Jesus Christ, upon his ascension to heaven, after his sufferings, death, and resurrection from the dead; when he was bid to sit down in human nature, at the right hand of God, in token of having done his work on earth to full satisfaction;

and in the relation of which David calls Christ his Lord; and is the reason of their being mentioned.