abe: The reason a sermon is always part of the service is that Paul told the young preacher Timothy to preach the word:
2 Timothy 4:2: Preach the word; be instant in season, out of season; reprove, rebuke, exhort with all longsuffering and doctrine.
/abe
I've heard that kind of sermon you are talking about, and never went back. There are many styles of giving a sermon. The Reformed seminaries train pastors to preach carefully through a book of the Bible. It takes years to get through a book but the sermons can be riveting, full of historical background, the present passage's relation to passages from other Bible books, as well as implications for the congregation. That kind of sermon can be too intellectual but it's always interesting.
Edited by Faith, : No reason given.