Since teachers in seminary lecture on their subject matter, that’s the model of communication that is set forth over three years for future preachers. But lecturing (though there may be a small unit of a sermon that might be such) isn’t preaching. A preacher must explain the text, but not take the entire time doing so. Having make it clear, his third person speaking ought to turn quickly to second person (“you”). When it does, and a Scripture is properly applied, he begins to preach. Do you preach or merely lecture about the text?