In 1917, Benedict XV wrote Humani Generis Redemptionem. It is a short encyclical that addressed a surprising contradiction: there seems to be more people preaching the Gospel than at any time in history, but when we look at the state of the world, there is a gradual slipping away from Christian virtue.
Pope Benedict asks if perhaps the Gospel is less effective in the modern wold: “Has the Word of God then ceased to be what it was described by the Apostle, living and effectual and more piercing than any two-edged sword? Has long-continued use blunted the edge of that sword?” However, this is certainly not the answer. He concludes that it is the preachers of the Gospel who are at fault. “If that weapon does not everywhere produce its effect, the blame certainly must be laid on those ministers of the Gospel who do not handle it as they should.”
For Benedict, this was not just another problem among the many problems that faced the Church at the time. He said it was a very grave matter “to bring back the preaching of the Word of God to the norm and ideal to which it must be directed.”
Citing the Council of Trent, the Pope asks bishops to only allow preachers to speak who “can exercise the ministry of preaching with profit to souls.” He defines this “profit of souls” not to elegance or popularity, but “spiritual fruit.” This, he says, is the purpose of preaching. Just like we don’t call someone a doctor who does not practice medicine, someone is not really a preacher unless they are a healer of souls–leading them to salvation and a deeper knowledge of God.
The rest of the encyclical talks preparation a preacher must have, the suffering they are willing to undergo, and the spirit of prayer they must live. The original is very short and well worth the time to read it: Humani Generis Redemptionem