Alan of Lille distinguished preaching from teaching by saying that one is public and the other private. Among other things, he wanted to deny that heretics ever preach, showing he had a higher view of preaching than of teaching, though he himself was also a teacher. Heretics carried on in private rather than in public, especially in an age that burned them at the stake. Alan, of course, did not want to cast any aspersions on the practice of burning heretics at the stake, but he raises an interesting question. What is also implied in his distinction is that the difference between preaching and teaching, in his mind, is one of situation: situation determined by quantities. Teaching involved at most a conversation, whereas preaching involved a greater audience.
And that is when rhetoric becomes obvious, isn’t it? You can’t speak conversationally in a large setting, not unless you have artificial amplification. And even that artificial amplification has its effect. I well remember the astonishing sense of watching a preacher continue in a large church after the sound system failed: he physically seemed to diminish. It suggests to me that rhetoric has a lot to do with what is fitting to the situation. It has to do with what is fitting to the situation because it is concerned with how one comes across, in other words, with the effect one has. It is about the consideration of the effect the way you approach and deliver your subject-matter will have on those who hear you.
Which is why you need rhetoric. You have to be conscious of it if you want to do it at all well, unless you naturally do it well. It requires consideration, and consideration beyond what you considering can come up with. And even if you naturally do it well, it is well to consider what is proper and improper not only in the aesthetic realm—which is important—but in the moral realm. If you don’t think about whether you ought to achieve things by one or another effect, if you don’t label certain approaches and understand clearly what you are doing, how will you confront your deceitful heart when you are proceeding by sensationalism, fearmongering, omitting crucial details and such unscrupulous means? If you can’t deal with it reasonably, if you don’t consciously think about it and humbly consult independent advice, are you likely to deal with it at all given what the human heart is?