This is a rhetorical question. It can be translated as "Why do they say" or "Let's think about them saying" or "I will talk about them saying." (See: [[rc://en/ta/man/translate/figs-rquestion]])
"King David's descendant." The word "son" is used here to refer to a descendant. In this case it refers to the one who would reign over God's kingdom. (See: [[rc://en/ta/man/translate/figs-synecdoche]])
This can be translated as "The Lord God said to my Lord" or "God said to my Lord." This is a quotation from Psalm [Psalms 110:1](../../psa/110/001.md) which says "Yahweh said to my Lord." But the Jews stopped saying "Yahweh" and often said "Lord" instead.
## my Lord ##
David was referring to the Christ as "my Lord."
## my right hand ##
The right side is the place of honor. God was honoring the Messiah by saying "Sit at my right hand."
## until I make your enemies your footstool ##
This is a metaphor. It can be translated as "until I make your enemies like a footstool for you" or "until I conquer your enemies for you." (See: [[rc://en/ta/man/translate/figs-metaphor]])
"so how can the Christ be David's son?" This is a rhetorical question. It can be translated as "This shows that the Christ is not merely David's descendant." (See: [[rc://en/ta/man/translate/figs-rquestion]])