Paul asks this question to show that there is no reason for people to boast about obeying the law. AT: "So there is no way that we can boast that God favors us because we obeyed those laws. Boasting is excluded" (See: [[rc://en/ta/man/translate/figs-rquestion]])
Paul asks and answers these rhetorical questions to emphasize that each point he is making is certainly true. You can translate this by including the words that Paul implies, and by using an active form. AT: "On what grounds should we exclude boasting? Should we exclude it because of our good works? No, rather, we should exclude it because of faith" (See: [[rc://en/ta/man/translate/figs-rquestion]] and [[rc://en/ta/man/translate/figs-ellipsis]] and [[rc://en/ta/man/translate/figs-activepassive]])
Here "faith" is an abstract noun that refers to the person believing in God. The "person" here is any person. This can be translated in active form. AT: "God justifies any person who believes in God" or "when God justifies a person, he does so because the person believes in God" (See: [[rc://en/ta/man/translate/figs-abstractnouns]] and [[:en:ta:vol2:translate:figs-activepassive]])