Because the Catholic Epistles focus on orthodox faith and morals, the Fathers drew on them as a means of defense against the rising challenge of heretics. This factor gave these letters a freshness and relevance to conditions in the fourth and fifth centuries that might otherwise seem surprising. Many of the Fathers unabashedly saw in them anticipatory attacks on Marcion and strong defenses against the Arians. They did so quite naturally because in their view truth was eternal and deviations from it had existed from the beginning. Above all, the Fathers found in the Catholic Epistles a manual...