Biblical Theology is a very fruitful field for preachers. Not every fruit is worth eating, of course, but there is real benefit to studying works in this field. To give a basic definition for the sake of this post: Biblical theology is the fruit of studying the Bible in such a way as to recognize the individuality of each biblical author, the progress of revelation over time and the unity of the canon resulting from the inspired nature of Scripture. My question today is simple, does our preaching honor these three aspects of biblical theology, or do we neglect one “side of the triangle?” Today we’ll consider the first “side of the triangle,” with the others to follow:
Individuality of each biblical author – The writings of John have a distinctive style, vocabulary and content when compared to the writings of Luke, or Paul, etc. How do we neglect this reality in our preaching? We do so by blending everything into the same, flat message. We do so by excessive cross-referencing to other authors without good reason. A high view of the Scriptures can easily lead to neglect of the individual styles and content of the human authors. Obviously we would affirm that John does not contradict Matthew, or Moses, for that matter. However, we may let our listeners down when we give the impression that the human author’s individuality does not shine through in their writings. In fact, we may be undermining the high view of Scriptures we affirm if we give the impression they were mere conduits for the dictation of God – a flawed understanding of inspiration!
Guidelines? Wherever possible, recognize and value the individuality of the human author when preaching a passage. Generally seek to demonstrate the flow of thought within the book, rather than demonstrating the theology of the passage through cross-referencing all over the canon. Perhaps consider how to preach the content of this passage using the vocabulary and style of this author (eg. I preached the resurrection passage in Luke in deliberately Lukan terms, rather than slipping into Johannine vocabulary or Pauline, 1Cor.15, argumentation.)
These are not hard and fast rules, just suggestions to help if this “side of the triangle” is being neglected in your preaching. Other suggestions? (The other two sides are coming, so please don’t get overly concerned that I haven’t emphasized the unity of the canon yet!)
Biblical Preaching 
I am not sure about this thought, maybe I need to study the idea a little more. Preaching the personalilty of Paul or John or Matthew, I am not so sure that is the point maybe you are making but nor do I understand why I should?
Perhaps “style” is a risky word to use. I should be preaching in my own “style” rather than acting. However, if our goal is to really effectively communicate the message of a passage, then it is a logical extension that we should consider how to explain the passage according to the vocabulary of that author wherever possible. For example, we can easily take a story in Luke and preach it in very Johannine terms – eternal life, believe, etc. Since individual vocabulary choices carry meaning with them, this can be important. I don’t know how many times I’ve heard the resurrection preached from Matthew, Mark, Luke, John, but really the explanation was Pauline (1Cor.15). This level of precision is certainly not a basic building block for beginner preachers, but it is a thought well-worth wrestling with for those of us with more experience. How committed are we to preaching a specific text? Committed enough to stay there? Committed enough to explain it as the author himself might, if he were here? We blend across authors by default and this can be helpful in one respect (the unity of the canon), but it can undermine attempts to really grasp the intent and content of the author of this specific passage. We shouldn’t explain Matthew’s use of “justification” in Paul terms. I could go on . . . this is good meaty stuff for us preachers to think through.