1. In the first place, S. Augustine continually remarks that the more accurate enucleation of true doctrine usually proceeded from the attacks of heresy; and this happened so continually that it seems to him a special instance of that law of divine Providence which educes good from evil. “If the truth,” says he, “had not lying adversaries, it would be examined with less carefulness,” and so “a question started by an opponent becomes to the disciple an occasion of learning.”(241) And he observes that “we have found by experience that every heresy has brought into the Church its own questions, against which the divine Scripture was defended with greater care than if no such necessity had existed.”(242) Thus the doctrine of the Trinity owed its perfect treatment to the Arian assault on it; the doctrine of penance to that of Novatian; the doctrine of baptism to those who wished to introduce the practice of rebaptising; even the unity of Christ was brought out with greater clearness by the attempt to rend it, and the doctrine of one Catholic Church diffused through the whole world cleared from its objectors by showing that the mixture of evil men in it does not prejudice the good.(243) And he illustrates his meaning by a very picturesque image: “When heretics calumniate, the young of the flock are disturbed; in their disturbance they inquire; so the young lamb butts its mother’s udder till it gets sufficient nutriment for its thirst.”(244) For the doctors of the Church being called upon for an answer supply the truth which before was latent. And there is no more signal instance of the great writer’s remark than himself; for the attacks of the most various heresies led him during forty years of unwearied mental activity into almost every question of theology.