Luther told stories in his sermons in an effort to break up the Medieval “imaginary” (to use Charles Taylor’s word) and replace it with a new understanding of the human relationship to God. The stories function in the space of and were designed to create a meta narrative:

“A metanarrative constitutes a fundamental view of reality; it lays down principles of interpretation; it forms the hermeneutic that guides the composition of new stories and the manner in which old stories are re-presented. It is not only, as a literalist might interpret “meta,” after the story, although it does help the narrator summarize what has been told and indicate to the hearers what they should make of the story. It also takes place before the story: it is a perception of ultimate truth that shapes the narrator’s selection of the stories to be recited, the emphases on various elements within them, and the significance assigned to the story and its parts.”

Kolb, Luther and the Stories of God.

It is important to realize that we utilize and thus portray a metanarrative whether we are conscious of this or not. 

No matter what preachers may think they are doing with their exposition, it is the metanarrative which controls the meaning of what they say. To give a trivial example, think of someone who says something is “good” when they mean it is bad. It is the surrounding story-not the words which control meaning.

Thus the preacher’s story – everything from how he publicly lives his life to the types of stories he tells in his sermon (are your stories always about yourself, always funny, etc) – and how the overarching story of Scripture comes through.