The churches of Christ are all autonomous.. there is no central government, or committee. Each assembly decides what is best for them. Smaller assemblies usually have "volunteer" preachers, or even itinerant preachers.
I imagine that most larger assemblies have a salaried preacher. The salary will go up, depending on the size of the congregation. I was a little surprised to learn how much our preacher was paid. Our congregation is just under 1000 members.
Also, our preacher is not a pastor. He is a younger man, with two young children.
I have mixed feelings about having a preacher who is also a pastor. Being a pastor should be almost a full-time thing.. or full time for whatever time the man has outside his secular job. Being a preacher IS a full time, paying job, for most preachers. They go to seminary, get degrees, advanced degrees, etc... and are hired by congregations specifically to bring good, Bible based lessons to the congregation. And most of them have a talent for public speaking. (not all, though...
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The churches of Christ are different from many other non-denom or even many denominations, in that a preacher (what most of you erroneously call a 'pastor') does not "run" a church. He is simply an employed preacher/teacher for the assembled body. Assemblies are "run" by elders and deacons..
In smaller assemblies, I imagine that one of the pastor/elders would bring a lesson/sermon to the assembly. After all, one of the required qualities of a pastor/elder is that he should be able to teach others.
In my way of thinking, that would be the ideal situation... no "paid" preacher, just individual members of the assembly giving sermons each week. But, let's face it... not everyone is good at that. I would not be good at it. I'm ok in personal, smaller settings, but to stand and simply expound on a topic for 30 minutes or so is definitely not my forte'....
As Dirty Harry said.... "a man's got to know his limitations"