The Rev. Dr. Frank Thomas asked me that question today. Actually, he asked the whole class of the preaching workshop I attended. The theme was the role of celebration in preaching.
He knows a thing or two about celebration preaching:
We also have to know ourselves.
If you preach from your deepest core beliefs about God, you won't have to write in the margins of your sermon "get loud here." You will be so tied to the meaning and message that you will speak with passion. You'll automatically get loud where you need to be loud and speak in a whisper at just the right moment.
If you ever do not know what to preach on, if you are lost or doubting, if you are in a personal crisis and don't know what message of Good News could possibly apply to this situation, Dr. Frank Thomas has a suggestion for where your sermon will come from.
"What do you most deeply believe about God? Preach that!"
I say, Amen.