At First Things, Carl Trueman shares a quote from John Henry Newman on the purpose of writing:
First, a man should be in earnest, by which I mean, he should write, not for the sake of writing, but to bring out his thoughts. He should never aim at being eloquent. He should keep his idea in view, and write sentences over and over again till he has expressed his meaning accurately, forcibly, and in few words. He should aim at being understood by his hearers or readers. He should use words which are most likely to be understood—ornament and amplification will come to him spontaneously in due time, but he should never seek them.
I agree with Newman and would, in fact, apply them to preaching as well!