There are two basic forms of preaching: expository and topical. Hughes Oliphant Old defines expository preaching as “the systematic explanation of Scripture done on a week-by-week…basis at the regular meeting of the congregation.” Expository preaching grounds the message in the text so that all the sermon’s points are points in the text, and it majors in the text’s major ideas. It aligns the interpretation of the text with the doctrinal truths of the rest of the Bible. And it always situates the passage within the Bible’s narrative, showing how Christ is the final fulfillment of the text’s theme.
By contrast, the main purpose of “thematic” or “topical” preaching is not the unfolding of the ideas within a single biblical text but rather the communication of a biblical idea from a number of texts. Topical preaching may have any one of several aims. It may be to convey truth to nonbelievers (evangelistic preaching) or to instruct believers in a particular aspect of their church’s confession and theology (catechetical preaching). Festal preaching helps listeners celebrate observances in the church year such as Christmas, Easter, or Pentecost, while prophetic preaching speaks to a particular historical or cultural moment.
I would say that expository preaching should provide the main diet of preaching for a Christian community. Why? Here is the main reason (though of course there are many others): Expository preaching is the best method for displaying and conveying your conviction that the whole Bible is true. This approach testifies that you believe every part of the Bible to be God’s Word, not just particular themes and not just the parts you feel comfortable agreeing with.
It is not enough to have a general respect for the Bible that you may have inherited from your upbringing. As a preacher or teacher you will come upon many difficulties in the Bible; and inevitably the biblical authors say things that not only contradict the spirit of the age but also your own convictions and intuitions. Unless your understanding of the Bible—and your confidence in its inspiration and authority—are deep and comprehensive, you will not be able to understand and present it convincingly. Instead of proclaiming, warning, and inviting, you will be sharing, musing, and conjecturing.
It is important to know not only in general that the Bible is true but also that in the Bible God’s words are identical to his actions. When he says, “Let there be light,” there is light (Genesis 1:3). When God renames someone, it automatically remakes him (Genesis 17:5). The Bible does not say that God speaks and then proceeds to act, that he names and then proceeds to shape—but that God’s speaking and acting are the same thing. His word is his action, his divine power.
So how do we hear God’s active Word today if we are not prophets or apostles? God’s words in the mouths of the prophets (Jeremiah 1:9-10), written down, are still God’s words to us when we read them today (Jeremiah 36:1-32). In other words, as we unfold the meaning of the language of Scripture, God becomes powerfully active in our lives. The Bible is not merely information, not even just completely true information. It is “alive and active.” (Hebrews 4:12)—God’s power in verbal form. It is only as we understand the meaning of the words that God names us and shapes us and recreates us.