Aeterna Dei Sapientia §27

²⁷ "It was due to his excelling virtue, his teaching, and his most vigilant zeal as shepherd of his people, that he won from our forefathers the title Great. In expounding the deeper mysteries of our faith and vindicating it against the errors that assail it, in imparting disciplinary rules and moral precepts, the excellence of his teaching is so radiant with the majestic richness of priestly eloquence and has so won the admiration of the world and the enthusiasm alike of Councils, Fathers and writers of the Church, that the fame and reputation of this wisest of popes can hardly be rivalled by any other of the Church's holy doctors." (22)