What is expository preaching? What are the duties of the pastor and the role of the congregation?
Expositional preaching has three main characteristics. First, the passaged that is preached on is a single passage rather than various passages put together. Second, the main point or theme of the sermon is derived from the theme or main point of the passage. That is, expositional preaching seeks to exposit the text that is preached. Third, expositional preaching is typically lectio continua—that is, it is preaching that consecutively works through passages of Scripture in their biblical context.
Here are two of my favorite definitions:
“Expository preaching is that mode of Christian preaching that takes as its central purpose the presentation and application of the text of the Bible. All other concerns are subordinated to the central task of presenting the biblical text. As the Word of God, the text of Scripture has the right to establish both the substance and the structure of the sermon. Genuine exposition takes place when the preacher sets forth the meaning and message of the biblical text and makes clear how the Word of God establishes the identity and worldview of the church as the people of God” (R. Albert Mohler Jr., He is Not Silent: Preaching in a Post-Modern World, 65).
“To expound Scripture is to bring out of the text what is there and it expose it to view. The expositor pries open what appears to be closed, makes plain what is obscure, unravels what is knotted and unfolds what is tightly packed. The opposite of exposition is ‘imposition,’ which is to impose on the text what is not there. But the ‘text’ in question could be a verse, or a sentence, or even a single word. It could equally be a paragraph, or a chapter, or even a whole book. The size of the text is immaterial, so long as it is biblical. What matters is what we do with it. Whether long or short, our responsibility as expositors is to open it up in such a way that it speaks its message clearly, plainly, accurately, relevantly, without addition, subtraction or falsification” (John Stott, Between Two World, 125-26).
Thus, pastors have the duty to communicate God’s transforming truth, exalt Jesus Christ, teach the Bible so that people understand and apply what God has said, and encourage conformity to Christ (see e.g. Neh. 8:7-8; 1 Tim. 3:2).
The duty of the congregation is to attentively and prayerfully listen to and seek to apply the word taught with reverence and humility realizing that the pastor is seeking their welfare (Heb. 13:17) yet always being discerning to ensure that what is said is in accord with the word of God (Acts 17:11).
 Cf. Gospel Centered Youth Ministry, 55.
Why are sermons such a big deal? The Bible tells us to sing as the gathered church. The Bible also tells us to celebrate the Lord’s Supper and baptisms. But why are sermons essential?
Sermons are essential because they teach God’s truth so as to exalt Christ, encourage and build up, and exhort the gathered church.
First, the teaching aspect of the sermon is important. Its importance is seen all over Scripture (e.g. Neh. 8:7-8; 1 Tim. 3:2). God has spoken and so helping people understand and apply the revelation from Him is life-changing. God’s people, however, are able to understand His truth. This is because all believers are indwelt by the Holy Spirit (Eph. 2:22; 1 Cor. 3:16; 2 Cor. 6:16), Jesus has made all those in Him priests (1 Pet. 2:5, 9; Rev. 1:5-6), and Scripture is clear on the things which are “necessary to be known, believed, and observed, for salvation” (The Westminster Confession of Faith, ch. 1). Qualified teachers are still vital, however, because sound (or healthy) doctrine is vital. That is, in part, why pastors must be “able to teach” (1 Tim. 3:2; 2 Tim. 2:24) and defend the truth (2 Tim. 2:25; Titus 1:9). We also see in Scripture that right teaching leads to maturity and the body of Christ being equipped for every good work. Believers may be able to subsist on milk but teachers are able to provide needed meat (2 Cor. 3:2; Heb. 5:12-13).
Second, communicating God’s truth in sermons is vital because the Bible is the authoritative word of God and it is uniquely profitable (2 Tim. 3:16-17). It is our sole authority for faith and practice. Scripture is a light (Ps. 119:105,130), a sword (Eph. 6:17), a hammer (Jer. 23:29), and a surgeon (Heb. 4:12). Scripture is more essential than bread (Matt. 4:4), better than gold (Ps. 19:10; 119:72), and we need it to live (Ps. 119:144). Scripture is perfect (Ps. 19:7), true (Ps. 19:9), pure (Ps. 19:8), and eternal (1 Pet. 1:25). Scripture contains the words of life (Jn. 6:68) and the words that are breathed out by God (2 Tim. 3:16). Scripture gives joy (Ps. 119:111; Jer. 15:16), makes wise (Ps. 19:7), equips (2 Tim. 3:17), guards (Ps. 119:9), guides (Ps. 73:24; 119:105), saves (1 Pet. 1:23), sanctifies (Ps. 119:9,11; Jn. 17:17), and satisfies because by it we know God (1 Pet. 2:3 cf. Ps. 16:11; Jn. 17:3).