This is pretty much our (Anne's and my own) understanding of preaching at Good Shepherd. Of course we don't get to preach as long as we would in a non-liturgical church, but the goal and purpose is the same even though we rarely meet it.
You can read John Piper's explanation of preaching here:
Preaching Is Expository
Expository means that preaching aims to exposit, or explain and apply, the meaning of the Bible. The reason for this is that the Bible is God’s word, inspired, infallible, profitable—all 66 books of it.
The preacher’s job is to minimize his own opinions and deliver the truth of God. Every sermon should explain the Bible and then apply it to people's lives.
The preacher should do that in a way that enables you to see that the points he is making actually come from the Bible. If you can’t see that they come from the Bible, your faith will end up resting on a man and not on God's word.
The aim of this exposition is to help you eat and digest biblical truth that will
* make your spiritual bones more like steel,
* double the capacity of your spiritual lungs,
* make the eyes of your heart dazzled with the brightness of the glory of God,
* and awaken the capacity of your soul for kinds of spiritual enjoyment you didn’t even know existed.