James describes a hypothetical situation where someone objects to his teaching in 2:14-17. James names this person "foolish man" in verse 20. The purpose of this hypothetical discussion is to correct his audience's understanding of faith and works. (See: [[rc://en/ta/man/translate/figs-hypo]])
James is describing a likely objection someone may have to his teaching. AT: "it is acceptable if one person has faith and another person does good deeds."
This is a rhetorical question used to scold the person who will not listen to James. AT: "You fool! You do not even want to listen to me prove that faith without works is useless." (See: [[rc://en/ta/man/translate/figs-rquestion]])