Not only do the best preachers deliver sermons and develop a point of view they also practice their sermons. This is something that every homiletic class (the fancy title for preaching class) in seminary teaches. Practicing sermons are vital to the delivery and to the development of the point of view. However, practicing sermons is not the same as rehearsing sermons.
One does not have to rehearse sermons, but they must be practiced.
Practicing sermons, or "practice what you preach", is the idea that we need to do what we preach not just speak it. So if you are a preacher that preaches about the need for reconciliation, then your sermons will be made great if you practice reconciliation. If you are a God accepts all people sort of preacher, then you should practice that sermon.
The beautiful part is that when you practice your sermons, then you will not have as much of a need to rehearse them. The sermon will come from your being and doing. The people can see your sermon each time you stand in the pulpit.
You can rehearse all you want, but the best preachers practice their sermons.
There is a great little story by Henri Nouwen (Time Enough to Minister, 1982) that speaks to the need to practice your sermons, even when you don't have time to rehearse them. It goes like this:
"Often we're not as pressed for time as much as we feel we're pressed for time. I remember several years ago becoming so pressed by demands of teaching at Yale that I took a prayer sabbatical to the Trappist monastery at Geneseo, New York. No teaching, lecturing, or counseling--just solitude and prayer.
"The second day there, a group of students from Geneseo College walked in and asked, 'Henri, can you give us a retreat?'
""Of course at the monastery that was not my decision, but I said to the abbott, 'I came here from the university to get away from this type of thing. These students have asked for five meditations, an enormous amount of work and preparation. I don't want to do it.'
"The abbot said, 'You're going to do it.'
"'What do you mean? Why would I spend my sabbatical time preparing all those things?'
"'Prepare?' he replied. 'You've been a Christian for forty years and a priest for twenty, and a few high school students wan to have a retreat. Why do you have to prepare? What those boys and girls want is to be a part of your life in God for a few days. If you pray half an hour in the morning, sing in our choir for an hour, and do your spiritual reading, you will have so much to say you could give ten retreats.'
"The question, you see, is not to prepare but to live in a state of ongoing preparedness so that, when someone who is drowning in the world comes into your world, you are ready to reach out and help. It may be at four o'clock, six o'clock, or nine o'clock. One time you call it preaching, the next time teaching, then counseling, or later administration. But let them be a part of your life in God--that's ministering."