"I would not hesitate to put in the first position: the loss of belief in the authority of the Scriptures, and a diminution in the belief in the Truth. I put this first because I am sure it is the main factor. If you have not got authority, you cannot speak well, you cannot preach. Great preaching always depends upon great themes. Great themes always produce great speaking in any realm, and this is particularly true, of course, in the realm of the Church. While men believed in the Scriptures as the authoritative Word of God and spoke on the basis of that authority you had great preaching. But once that went, and men began to speculate, and to theorise, and to put up hypotheses and so on, the eloquence and greatness of the spoken word inevitably declined and began to wane. You cannot really deal with speculations and conjectures in the same way as preaching had formerly dealt with the great themes of the Scriptures. But as belief in the great doctrines of the Bible began to go out, and sermons were replaced by ethical addresses and homilies, and moral uplift and socio-political talk, it is not surprising that preaching declined."
D. Martin Lloyd-Jones, Preaching and Preachers, p. 13.