Gordon Cheng raises this question (HT: Colin Adams) as part of a brief post on a passage from Richard Baxter’s Reformed Pastor. Cheng says,

I’ve never really agreed with the evangelical emphasis on preaching, and never quite understood how evangelicals make so much more of this than of other forms of teaching. It seems to me that the emphasis on public preaching, or should I say perhaps ‘pulpiteering’—as against private and personal ministry through, for example, conversation or Bible study groups—is quite unbiblical.

The practical reason that evangelicals still emphasize preaching, to the degree that emphasis still exists, is because they haven’t yet rid themselves of the every last vestige of the theology, piety, and practice of the Reformation or the original evangelicalism (as distinct from modern evangelicalism).

The original evangelicals, i.e. the Protestant Reformers emphasized the public proclamation of the Word (law and gospel) because they were convinced from Scripture that God has made promises specifically to use and bless the preached gospel (Rom 10). We summarize this understanding of the preached gospel by speaking of the preaching of the gospel as a “means of grace” (medium gratiae). It is our understanding of Paul’s teaching in Romans and elsewhere (e.g. 2 Tim 4:2) that the Spirit of God operates with and through Word (in the law) as it is preached to convict sinners of their sin and jeopardy before the all-holy God and through the Word (in the gospel) to raise them to life (regeneration), to give them faith, and to unite them to Christ.

Thus, in Heidelberg Catechism Q. 65 we confess that the Holy Spirit “works faith faith in our hearts through the preaching of the Holy Gospel and confirms it through the use of the holy sacraments.” We have a high view of preaching as a means of grace because Paul had a high view of the “foolishness” of gospel preaching (1 Cor 2). It doesn’t seem like it ought to “work” and if you’re looking for big numbers then call Bill Hybels or Bob Schuller. They know how to pull a crowd. If you want to know about preaching, however, look at Paul at Mars Hill. He preached the law and then he preached the gospel. Did he get a great response? Well Dennis (Dionysius) and a few others (Acts 17:34) followed him. That’s what happens sometimes. The Spirit blows where he wills (John 3).

What’s the big deal about preaching? It’s the vehicle, the instrument, the means by which God the Spirit brings his elect to faith. Otherwise, it’s not a big deal.