In his book on Preaching Without Notes (1875), Richard Storrs reminds us of the simple necessity of clearing out the brain before preparing a similar sermon. He states:
Discharge your mind of the sermon when once you have have preached it so keeping the mind free and open for other subjects succeeding that one. I cannot give you any rule by which to do this. I only know that it can be done, though it is not easy; that the habit of doing it can be formed like [a] habit….
The lawyer does it, all the time. All sorts of cases come successively before him, and each, in its turn, fully occupies his mind: cases of insurance; cases involving felony—murder, theft, forgery, battatry [sic], libel, or what not; cases of patent-rights; cases involving the title to lands; horse-cases perhaps. While he is arguing one, his thoughts are full of it. The next eliminates it wholly from his mind; and the one is forgotten when the other is before him.
A minister must learn to do much the same thing. It is not easy, as I said. …I found that one great secret of success in doing what was needed was to take a second subject very different from the first: then the expulsive power of the new subject, occupying the thoughts, freed them from embarrassing reminiscences of the other. If you have preached on a theme of doctrine, for example, in the morning, take some point of Christian practice for your theme in the evening. If one discourse is preceptive and hortatory, let another be narrative, in its structure. If one is closely argumentative, let the next be a careful yet free exposition of a parable or a psalm. So you will find that the mind releases itself from the one subject, by taking another entirely distinct; its natural resilience is helped and stimulated, and you cease to be weighted with your previous processes.
In this way, or some other, you must secure the result which I indicate. Otherwise, you will be all the while in danger of repeating proceeding trains of thought, of applying the intellectual methods proper to one subject to another widely different, and of wholly failing to widen and enrich your mind. You will be likely, even, to get by degrees a set of pet subjects, of recurring phrases, and of familiar illustrations; and to feel yourself, and to make your people feel as well, that your mind is becoming narrow and unproductive through your method of preaching. (pp. 56-58)
I don’t know how it is with you, but I don’t preach Sunday morning, Sunday evening and Wednesday evening with a Bible study in between. I preach, basically once a week, barring weddings or funerals. And the small group lesson I prepare and teach is based on the sermon material! I suspect, however, that the preparation of some lesson on a clearly different subject would serve the purpose.
A common sense suggestion, but not one I would have put into words like this little book…132 years old!!