Any true definition of preaching must say that that man is there to deliver the message of God, a message from God to those people. If you prefer the language of Paul, he is 'an ambassador for Christ'. That is what he is. He has been sent, he is a commissioned person, and he is standing there as the mouthpiece of God and of Christ to address these people. In other words he is not there merely to talk to them, he is not there to entertain them. He is there - and I want to emphasize this - to do something to those people; he is there to produce results of various kinds, he is there to influence people. He is not merely to influence a part of them; he is not only to influence their minds, not only their emotions, or merely to bring pressure to bear upon their wills and to induce them to some kind of activity. He is there to deal with the whole person; and his preaching is meant to affect the whole person at the very centre of life. Preaching should make such a difference to a man who is listening that he is never the same again. Preaching, in other words, is a transaction between the preacher and the listener. It does something for the soul of man, for the whole of the person, the entire man; it deals with him in a vital and radical manner.I remember a remark made to me a few years back about some studies of mine on “The Sermon on the Mount.” I had deliberately published them in sermonic form. There were many who advised me not to do that on the grounds that people no longer like sermons. The days for sermons, I was told, were past, and I was pressed to turn my sermons into essays and to give them a different form. I was most interested therefore when this man to whom I was talking, and he is a very well-known Christian layman in Britain, said, "I like these studies of yours on “The Sermon on the Mount” because they speak to me.” Then he went on to say, “I have been recommended many books by learned preachers and professors but,” he said, “what I feel about those books is that it always seems to be professors writing to professors; they do not speak to me. But,” he said, “your stuff speaks to me.” Now he was an able man, and a man in a prominent position, but that is how he put it. I think there is a great deal of truth in this. He felt that so much that he had been recommended to read was very learned and very clever and scholarly, but as he put it, it was “professors writing to professors.” This is, I believe, is a most important point for us to bear in mind when we read sermons. I have referred already to the danger of giving the literary style too much prominence. I remember reading an article in a literary journal some five or six years ago which I thought was most illuminating because the writer was making the selfsame point in his own field. His case was that the trouble today is that far too often instead of getting true literature we tend to get “reviewers writing books for reviewers.” These men review one another's books, with the result that when they write, what they have in their mind too often is the reviewer and not the reading public to whom the book should be addressed, at any rate in the first instance. The same thing tends to happen in connection with preaching. This ruins preaching, which should always be a transaction between preacher and listener with something vital and living taking place. It is not the mere imparting of knowledge, there is something much bigger involved. The total person is engaged on both sides; and if we fail to realize this our preaching will be a failure.
— D. Martyn Lloyd-Jones, Preaching and Preachers