Why do Preachers Preach???

I wanted to ask the believing church body, why do preachers preach? Other than to deliver a message on a subject that can be utilized as a teaching lesson to be sold in CD or DVD format, what is the purpose of the sermon???

Preachers are supposed to be Shepherds guiding and leading their flock somewhere. Where do they lead them???

I listen and watch many church programs where often times preachers condemn and accuse their congregation of not having a relationship with Christ. They accuse the church body of living in the world, of not having faith in God, of living in sinful relationships, and on an on..... Am I just getting the 30 min sermon and missing the complete picture or is this the true snapshot of what a preacher does?? What are your beliefs???