7 "With profit to souls," well note that the word which expresses the rule does not mean eloquently or with popular applause, but with spiritual fruit. This is the end for which the ministry of the Divine Word is instituted. If now you would have Us define more exactly the qualifications of those who are really to be considered fit, We answer: those in whom you find the signs of a Divine vocation. Whatever is required for admission to the priesthood, is likewise needed if one is to be considered eligible and fit for the office of preaching. "Neither doth any man take this honor to himself, but he that is called by God." [ Heb . v:4] Such a vocation is easily determined. For Christ Our Lord and Master, when about to ascend into heaven, did not by any means bid His Apostles forthwith go into diverse places and begin their preaching: "But stay you in the city," He said, "till you be indued with power from on high." [ Luke xxiv:49] This, therefore, is the sign by which you may know whether any one is Divinely called to this task: if he "is indued" with power from on high. What this means, Venerable Brethren, may be gathered from what took place in the case of the Apostles as soon as they had received power from on high. For when the Holy Spirit had descended upon them, not to mention here the wonderful gifts with which they were endowed, they were transformed from frail unlettered disciples into learned and perfect men. If a priest therefore has the required knowledge and virtue together with those natural qualifications necessary, without which he would be tempting God, he may be considered as having a true vocation for the office of preaching and there is no reason why he may not be admitted by the Bishop to this ministry. Such is the meaning of the Council of Trent when it decrees that the Bishop is not to permit any to preach unless they are "of approved virtue and learning." ( Loc cit.) Wherefore it is the duty of the Bishop long and thoroughly to examine those who are to be entrusted by him with the function of preaching that he may find out the nature and extent of their learning. If any one acts carelessly and negligently in this duty, he clearly offends in a grievous matter, and on him will fall the responsibility of the errors which the untrained preacher may spread or of the scandal and the bad example which the unworthy one may give.
Source: Humani Generis Redemptionem (Vatican.va)