Preachers may faithfully preach thematic and topical sermons that explain the Bible. They are certainly free to preach sermons on particular texts of Scripture without preaching through whole books of the Bible.
But here are some reasons that preaching through whole books of the Bible is valuable.
1. Preaching through books of the Bible forces us to deal with everything the Bible has to say. Some passages of Scripture are hard to understand, and some are hard to believe. That fact can tempt preachers to preach the easier passages and neglect the harder ones. But, if we preach through whole books at a time, then we have no choice but to deal with the difficult texts, and wrestle with their meaning, and application, even if their meaning and application are difficult or uncomfortable to us.
2. Preaching through whole books at a time guards us against misinterpreting the Bible because it forces us to deal with every verse of the Bible in its own context. It‘s possible to take a verse out of context and make it say what we want it to say. That can even happen inadvertently. But it is much more difficult to misinterpret the Bible when we study its words and phrases in the context of the message of the book in which they are found.
3. Preaching through books of the Bible keeps us away from hobby horses or favorite themes. It would be easy to find a few encouraging things or group distinctives in Scripture and restrict our preaching to those. But if we study through whole books at a time, then we get exactly the balance that God thinks is appropriate, perfectly and proportionately emphasizing God’s character, judgment, grace, the cross, the call to faith and repentance, how to live as Christians, the church, heaven and hell, etc.
4. Faithful preaching through whole books of the Bible is centered on Christ and redemption in Him. When expository preaching through books of Scripture is done correctly, it reveals a unity of divine purpose for the salvation of sinners in Christ. The expository preacher preaches not just portions of the Bible but the whole Bible in every sermon. This means that the law and the gospel are always present. Many sermons today are full of powerless platitudes, which give no true comfort, and moralisms, which bind up the conscience. But, expository preaching drives the preacher to see all doctrine and law as grounded in the person of Jesus Christ.
5. Preaching through whole books allows the Holy Spirit, who wrote Scripture, to set the agenda every Sunday. Preaching this way allows us to study and apply what God said in the order in which God said it. The expository preacher cannot come to the pulpit as a master who sets the agenda for the church each Sunday. Rather, he comes as a slave to God’s agenda. That is beneficial both to the preacher and to the congregation. The role of the preacher is not that of a chef, but of a waiter, who simply serves the food that God has prepared for His people.
6. We should preach through whole books at a time because every word of the Bible is true. If every word were not true, then we might pick and choose among texts of Scripture, choosing to preach and study what we believe is true, while leaving the rest. But, since every word of the Bible is true and breathed out by God for our sanctification, we ought to preach every word of the Bible.
7. Preaching through books of the Bible allows us to think God’s thoughts after him. If we work through entire books, then we are enabled to follow God’s own train of thought and logical argument as it moves through a book. The Bible is the mind of God revealed, and if we would know God’s mind, we must know what this book says in the order in which it says it.
8. Preaching through books of the Bible trains a congregation to correctly handle the Word of God, and it teaches them to recognize faulty interpretations. When a congregation is used to hearing solid exegesis, which involves carefully studying the historical background of a text, the lexical meanings of individual words, grammar, syntax, and analysis of the author’s flow of thought in each pericope and book, they become better equipped to study and apply the Bible in their own personal and family devotion to Christ.
9. Preaching through whole books of the Bible places divine limits on the authority of the preacher in the pulpit. If a pastor is not preaching through books of the Bible, then he is free to find any set of themes or sub-themes he pleases, string them together in any way he pleases, and make any doctrinal or practical point he pleases. This is the strategy of cults and false teachers. It is also the strategy of consumer driven churches that are more focused on numerical results and money than divine truth. In contrast, the expository preacher is a slave to the text and the congregation is trained to believe and do only what is plainly established from the text of Scripture. The Bible must constrain the pastor. The pastor must never constrain the Bible.
10. Preaching through whole books builds up the pastor in maturity. When a pastor commits himself to expository preaching, he cannot be a lazy preacher. He is forced to work hard to mine meaning out of the text and to make application. It gloriously chains him to his desk where he is forced to study Scripture. This is good for a pastor’s own sanctification and therefore good for the sheep he shepherds because a pastor can only lead God’s people to the degree that he loves and delights in the Lord.
11. Preaching through books of the Bible builds an appetite for the Word of God. When genuine believers are fed the Word of God, their hunger for it is not satiated; rather, it is deepened! Pastors who preach the Bible grow in their hunger for Scripture. Congregations of believers who hear the Word preached hunger for more of it.
12. Preaching through biblical books educates pastors and congregations doctrinally. In our current context, much preaching is void of doctrinal content. But the Bible is full of it. We desperately need to return to expository preaching so that the church can recover its comprehension of the Bible’s robust doctrine.