During a Q&A, I asked him how long it to prepare sermons well. His answer has stuck with me:
If you're preaching every Sunday to the same group of people, you need to be at three stages all the time. You need to be thinking about what comes six months from now. You need to be beginning to start to read the text so you become the master of the text while you do the other.
So you have that part that's going on for the future. Then you have the part where you've mastered the text and you're raising questions and making decisions about what you're going to add. Then you've got the one you're going to preach on Sunday.
On average, it's about 8-10 hours to do that for one sermon…I would view it as the highest value priority you have. Please cancel the service before you ever walk into a pulpit unprepared. You know what the third commandment is? Thou shalt not take the name of Yahweh your God for useless purposes. I've heard that violated in sermons when pastors got up ill prepared, invoked the name of God, and dropped it all over the place. I've heard that violated in pastoral prayers. I violate it in my own prayer life.
I made a commitment in my first pastorate that I would never walk in the pulpit unprepared. I did have to cancel two services early on where I had made serious mistakes.