14 The first lesson, therefore, that We learn from St. Paul is how well prepared and equipped he was for preaching. But We do not refer now to the learned studies he had assiduously pursued under Gamaliel. For the knowledge poured into his soul by revelation dimmed and nearly eclipsed the knowledge he had acquired by his own efforts, though that the latter knowledge was of no little value to him is clear from his Epistles. Learning, as We have said, is absolutely necessary for the preacher, for if he is without the light of learning he easily falls into error, since "Ignorance is the mother of all errors," as the Fourth Lateran Council so truthfully observes. We would not be understood, however, to mean every sort of knowledge, but only that which it becomes a priest to possess, that is to say, the knowledge, to phrase it briefly, which consists of a knowledge of self, of God and his duties. For self-knowledge, We maintain, will lead a priest to renounce his own advantage. The knowledge of God will lead him to make everyone else know and love God, and the knowledge of his office will lead him to discharge his own duties and to teach others to do theirs. If he lacks these three kinds of knowledge, whatever other learning he has, will only puff him up, and will be useless.
Source: Humani Generis Redemptionem (Vatican.va)