11 Not all however who depart from the right rule and norm, Venerable Brethren, are seeking for nothing but popular applause in their preaching. Frequently the preachers who avail themselves of these devices do so to attain some other and even less honorable object. Forgetting the saying of Gregory: "The priest does not preach that he may eat, but should eat that he may preach," [In I Regum , lib. iii], there are not a few who, because they think that they are unsuited for other labors by which they might be decently supported, take to preaching, not that they may worthily exercise the sacred ministry, but to make money. We therefore see them devoting all their attention not indeed to finding where greater fruit for souls may be hoped for, but where preaching reaps a more lucrative return.
Source: Humani Generis Redemptionem (Vatican.va)