Here "righteousness of the faith" means that God considered him to be righteous. Alternate translation: "a visible sign that God considered him righteous because he had believed in God before he was circumcised" (See: [[rc://en/ta/man/translate/figs-explicit]])
You can translate this in an active form. Alternate translation: "This means that God will consider them righteous" (See: [[rc://en/ta/man/translate/figs-activepassive]])