Preaching is the proclamation of God's Word by God's ambassador to people. True biblical preaching is the proclamation of God's Word from the actual words of God in the Scripture, for Scripture is the authority for the Christian mind and life. As such, it is very important how preaching is to be done, for, as the proclamation of God's Word, it is supposed to be authoritative, bearing upon all who hear it.
There are many ways preaching has been done throughout church history, some good, some not so good. But what I want to focus on here is a certain type of preaching that is practiced among those who focus on dogmatic theology, and thus the preaching can be called "dogmatic preaching." Such preaching often utilize a text of Scripture and exposit it based on theological concerns that have some relation to the text. In such preaching, the historical progression of revelation often takes a back seat, if taken into account at all. The text becomes a focus for theological consideration, and after the doctrines that have some relation to the text have been expounded, then application is made of these doctrines to its hearers.
Just as a caveat, this is not the same a preaching doctrines from the text. The difference is that dogmatic preaching downplays redemptive historical progression and concerns, if mentioned at all. Doctrinal preaching preaches doctrines that are shown to arise from the text, while dogmatic preaching uses the text like source material (if I may put it this way) for doctrines.
Just from the description and the contrast, it should be clear why dogmatic preaching is a problem. Assuming that the doctrine expounded is correct and orthodox, what is unclear is how the doctrine is actually biblically derived. The goal of preaching is to proclaim God's Word, but for that to be the case, what is proclaimed must be perceived to be from the Scriptures. But if one downplays the immediate context of the text, and omits the progressive nature of redemptive historical revelation, how can the doctrines being expounded be seen to be derived from the text, instead of being read into the text? If one flattens the text of Scripture such that there is no difference in kind when one preaches from the Old in contrast to from the New Testament, then the Scripture is used as a dogmatic source-book instead of revelation in history. Scripture loses its historical nature, and become transcendent (instead of revealing transcendent truths), as if the Bible were dropped directly from heaven to earth.
As a Westminster graduate, I obviously prefer redemptive-historical Christ-centered preaching, although not necessarily owning to anything and everything that calls itself by that name. I do not know if that is the best way of preaching, but what I do know is that, whatever style of preaching is used, the truths proclaimed must be seen to be derived from the text of Scripture. Failure to show how that is the case will at best not teach the hearers how to handle and interpret Scripture correctly, and at worst promote falsehood.