In the culture of that time, a father was more respected than a son. David's us of the title 'Lord' for the Christ implies that he was greater than David. (See: [[rc://en/ta/man/translate/figs-explicit]])
"so how can the Christ be David's son?" This can be a statement. Alternate translation: "and this shows that the Christ is not merely David's descendant" (See: [[rc://en/ta/man/translate/figs-rquestion]])