“Sermon” is a common enough word, and it’s used in lots of different ways. We gain something by examining the word a little more clearly though.
In my view, a sermon is a moment that occurs when a person leads a worshipping congregation in listening to the word of God. That definition excludes some things that we commonly call sermons, but puts a little more shape on the essence of the practice.
First, note that what I’m calling the sermon refers to the moment itself; the moment in which the congregation receives the word of God. There is a distinction between the moment itself and a couple of things which we might commonly call a sermon, such as the manuscript that is used to prepare for the moment, or perhaps an audio recording of the moment. Those things are artifacts of the moment, but they are not the thing itself.
The thing itself is the moment when the word is preached and received by a worshipping, gathered church. That context is the second critical feature, and it is at the heart of the difference between a sermon and an essay, or even a speech. A sermon is a moment shared by a group of believers who are worshipping—they’re engaging in the practice of submitting themselves to God. They are particularly primed to receive the word because of their worship posture, and the presence of the spirit in the congregation.
This “moment” based description of the sermon’s essence also holds another way that sermon differs from other speech acts: because it is in the context of worship, it is given in a space in which all present—speaker and hearers—are subjecting themselves to God. The preacher is just as subject to the word proclaimed in the sermon as the hearers. The word is for the whole gathered church, including the preacher! Indeed, the same spirit which moves the preacher to preach is also moving the church to receive the word! As a part of the congregation, the preacher does not stand apart, delivering a word as an outsider. Rather, it is as a part of the body that the preacher speaks, and necessarily the preacher must receive the sermon along with the rest of the congregation.
I know it’s quibbling, but If someone sends me a document, and says “Hey, read this sermon.”, in my own head I think it’s important to expand the shorthand a bit, because I don’t think that technically, I can read the sermon either before or after it’s moment. I can read the manuscript of the sermon, and I think maybe very usefully. But it’s not the same as the thing that happens when the church gathers together, and listens for a word from God.
Most of the time, when men become elders, they have very little idea of what things are going to be like. What should they expect in meetings? What’s expected from them outside of the meeting room? What kinds of questions are people going to start asking them that they never would have heard before? What do you do when your thoughts are on the fringe? It can all be shocking at first, and it takes a little while before it begins to feel somewhat normal. I’ve heard a lot of men say it was at least six months or a year before it felt normal to them—even two years is common!Typically, churches add elders in batches, and since a new batch can take a little while to adjust, they often assimilate into the way the group already does things, going with the flow while they learn to swim. Commonly being a part of an eldership is a moderating force on individuals, bringing them towards a center of thought. That’s mainly healthy and appropriate, part of the way the Spirit runs the church, but there is at least one by product of that process which is potentially negative. 
Steven Hovater 