Bible in the driving seat?

Enjoyed a stunningly helpful and refreshing lecture from David Jackman at the Proclamation Trust's Evangelical Ministry Assembly.

He had a particularly helpful illustration on the difference between preaching that is expository and preaching that merely delivers our theological framework.

Is the Bible in the driving seat for the sermon - it decides the course the sermon takes?
Or is the Bible in the passenger seat? A useful point of reference, but ultimately we decide where the car goes, not the Bible.

I'm sure that oversimplifies things slightly, but a helpful illustration nonetheless