Is there a formula for deciding what to preach?
There is no “formula” for deciding what to preach and when to preach it, but such a decision should be guided in both the long and short-term by God’s openly stated goals in this world: to glorify Himself, and to do so by growing the church of Jesus Christ both in number and in spiritual maturity. Since it is God alone who can accomplish this two-fold growth, and since He has already declared that He will use the God-breathed Scripture (2 Timothy 3:16) both to “make you wise for salvation through faith in Christ Jesus,” (2 Timothy 3:15) and to “thoroughly equip the man of God for every good work” (2 Timothy 3: 17), the preacher’s main job is to open that Scripture up to his people clearly and effectively week by week. Since “ALL Scripture is useful” for these two forms of growth, and especially for glorifying the God who alone makes things grow (1 Corinthians 3:7), it doesn’t matter as much what you preach as HOW you preach.
Preach always in such a way that God is glorified as a majestic, powerful, sovereign Emperor who is the “shield and the very great reward” of His people (Genesis 15:1 . . . the very chapter in which Abram is justified by faith!). Preach always in such a way that God’s words are made clear and God’s message comes straight from the text. Charles Spurgeon had inscribed on his pulpit so only he could see it, “Step aside, sir, that they may see Jesus.” To that marvelous concept I would add, “Step aside, sir, that they may understand God’s word.”
Having given that general exhortation, however, there are some guidelines for long-range planning of preaching which depend upon the maturity of your congregation. If your congregation is new to faithful expository preaching, try to give them a balanced diet of various genres of Scripture over your first two years or so: some Old Testament history, some Gospel, some New Testament epistle, some prophetic books, some Hebrew poetry. Do this by expositing specific books for a few months and moving on. Get this book (or section of a book) right, then go to the next book (or section).
This avoids the danger of topical preaching in which you are merely opening your mind on prayer, evangelism, stewardship, family issues, etc. Topical preaching is the opposite of expository preaching, for you are making the Scriptures say what you think they say, rather than letting them simply speak for themselves. Amazingly, if you simply move passage by passage through various books of the Bible, in two years’ time, you will hit almost every key topic they need to hear, and many of them several times.
As your congregation gets more acclimated to careful expository preaching, you may want to settle in to a more detailed and lengthy handling of a particular book of the Bible. Even there, however, it’s probably best not to get too bogged down. It’s easy to begin preaching careful verse-by-verse exposition, but end up being topical because each verse opens up its own topic. This is to be avoided. Also, try to give the people a sense of the majestic grandeur of God’s whole revelation to humanity: how this passage fits into the whole revelation of God.
One final word concerns “emergency” situations. There may well be some immensely pressing event that comes into the life of your congregation which forces you to leave your sermon series for a time to address that situation. Perhaps a flood has left half of them homeless; perhaps a war has broken out which is claiming the lives of their children; perhaps they are farmers and a blight has destroyed their livelihood. This is not some “current event” which people are talking about, but something which affects their very lives. Then it may be wise to address it from God’s Word. But this is the exception rather than the rule. For the most part, settle in and preach passage after passage faithfully as the Holy Spirit leads you from book to book for however many weeks He leads you to stay there. Pray and ask for the specific books and the number of weeks. His guidance and your faithful exposition of the series of texts to which He guides you will feed Christ’s lambs the nourishment they need.
Some recommended books on this:
John R.W. Stott, The Preacher’s Portrait, (Grand Rapids, Eerdmans, 1979);
D. Martyn Lloyd-Jones, Preaching and Preachers (Grand Rapids, Zondervan, 1972);
John MacArthur, “Preaching” in his Rediscovering Pastoral Minisry: Shaping Contemporary Ministry with Biblical Mandates (Dallas, Word, 1995), pp. 250-261.