David didn't go up to heaven. So he wasn't talking about himself when he said, “The Lord told my Lord to sit at his right side,
The LORD said to my Lord, “Sit at my right side, until I make your enemies into a footstool for you.”
The Holy Spirit led David to say, ‘The Lord said to my Lord: Sit at my right side until I make your enemies into a footstool for you.’
No one has gone up to heaven except the Son of Man, who came down from there.
until he made my Lord's enemies into a footstool for him.”
Christ will rule until he puts all his enemies under his power,
God has put all things under the power of Christ, and for the good of the church he has made him the head of everything.
God never said to any of the angels, “Sit at my right side until I make your enemies into a footstool for you!”