Teaching the Trinity through Expositional Preaching
The Trinity is one of the most central and crucial Christian doctrines; it is also one of the least prooftext-able. This presents a special challenge for preachers who, like me, are committed to preaching sequentially through books of the Bible. How can you teach your people the Trinity through expositional preaching when you so rarely encounter anything like a full statement of the doctrine in a single passage? When the Trinity does break the surface of the text, how can you guide your people into the doctrine’s depths without drowning them in detail?
What follows are five simple suggestions for how you can teach the Trinity through expository preaching.
1. Find other venues for heavy lifting.
First, find other venues for heavy lifting. In what other contexts can you teach as much Trinitarian doctrine as your people can digest? Adult Sunday school? Midweek Bible study? A Sunday night doctrine series?
I’m not saying you have to keep heavy doctrine out of the Sunday morning expositional meal. I am saying that your congregation will be better able to digest the meatier parts of that meal if you regularly supplement it. For instance, my church regularly teaches a 26-week systematic theology Core Seminar, and a few years back I delivered a one-off “elder address” on the role of Psalm 110:1 in the New Testament, which mined many Trinitarian veins.
Here would also be a good place to mention that book giveaways go a long way. Lately I’ve been giving away Scott Swain’s The Trinity: An Introduction like hotcakes.
2. Double click on pregnant phrases.
Second, double click on phrases that are pregnant with Trinitarian implications. While few New Testament passages present anything like a complete statement of the Trinity in brief, hundreds of them offer a window into the doctrine. Or, to put it the other way around, hundreds of passages in the New Testament imply the Trinity and are only fully intelligible in light of the Trinity. So, when you encounter one of these phrases, linger long enough to trace the path from text to Trinity.
If you have a gift for concision, you might be able to pull this off in a single sentence. For instance, just three days ago as of my writing, the senior pastor of my church, Mark Dever, preached Ephesians 5:5–6. Here is what he said about the phrase “the kingdom of Christ and God”: “The single King of the single kingdom is the Triune God.” That sentence packs a lot in, and you could spend a lot of time unpacking it. But you don’t have to. You can leave it sealed up as a gift for the members of your church to unwrap later through prayer and meditation. If you were to fully unfold the theological implications of the fact that a kingdom is ruled by a single king, and of the “and” between “Christ” and “God,” you would uncover the whole doctrine of the Trinity. But I’m not saying you have to do all that, at least not in every sermon. Instead, double-click on the phrase and leave a Trinitarian bookmark that can focus your members’ attention the next time they browse through Ephesians.
3. Practice “Iceberg Exegesis.”
Jonathan Pennington, one of my New Testament professors in seminary, often warns against “Viking Exegesis”: plowing in, pillaging the text to get whatever you want from it, and rushing home with your ill-gotten spoils. In keeping with Nordic, maritime themes, but offering a positive alternative, I want to commend what I call “Iceberg Exegesis.” Iceberg Exegesis recognizes that, as we saw in the previous point, the Trinity often breaks the surface of the text in a brief phrase or assertion. When it does, the doctrine is truly present, but most of its glorious hulking mass is hidden beneath the surface, as the presupposition that alone can make sense of the text’s above-water shape.
So, one of your jobs as an exegete is not only to point to the tip that everyone can see, but to map the theological iceberg beneath. For instance, consider the simple phrase with which Paul begins his benediction in Ephesians 1:3, “Blessed be the God and Father of our Lord Jesus Christ.” This text names two relations in which God the Father stands to his Son, our Lord Jesus Christ. The Father is both Christ’s Father and his God. How is it that God is Christ’s God? God is Christ’s God insofar as Christ became man for our salvation, and thus stands where we do in relation to God: as a creature (though not only a creature). How is it that God is Christ’s Father? That simple phrase vaults us into eternity, into what Fred Sanders calls “the happy land of the Trinity.” Think away creation, fall, and incarnation. Think away everything that is not God. Now all you have left is God. And the God you are left with is not a mere monad, but a Father eternally begetting a Son, and a Father and Son eternally breathing out their Spirit.
Another way to describe Iceberg Exegesis is to say that your job as an expository preacher involves not only explaining the sense of the text but, in a suitably simple and modest manner, analyzing its theological grammar. For instance, we can say that Ephesians 1:3 speaks of Christ in two ways: as man, Christ has God as his God; as God, Christ is the eternal Son of the eternal Father. In other words, the hypostatic union, in which the Son became man without ceasing to be God, is a theological structure that enables us to make sense of both phrases.
Similarly, in order to discern the sense of “Father” in Ephesians 1:3, we need to recognize that Scripture speaks both of what all three divine persons have in common, and what distinguishes them. What they have in common is the single divine nature: the Father, Son, and Spirit each fully possess all that makes God God. But Scripture also speaks of what distinguishes the divine persons: these distinguishing characteristics are the divine persons’ eternal relations of origin. The Father eternally begets the Son and not vice versa; the Father and Son eternally spirate the Spirit and not vice versa. This might seem a bit abstract and heady, but look again at Ephesians 1:3. When Paul says that God is the “Father” of the Lord Jesus Christ, he speaks in a relational register. He refers to the Father and the Son in a relative manner, naming the relation in which they subsist. In other words, to borrow Augustine’s phrase, “Father” speaks of God not “substance-wise” but “relation-wise” (see his De Trinitate V.1–3).
What’s the biblical evidence for the Trinity? In one sense, it boils down to this: Scripture speaks of God in two ways—common and proper, substantial and relative. Everything Scripture says about God fits into one of those two folders. And, taken together, those two folders simply are the doctrine of the Trinity.
I’m not saying you need to trot out all these fancy words whenever Scripture says “Father” or “Son.” What’s most important is that you understand the theological grammar, and that your explanation of the text accords with it.
4. Use Trinitarian shorthand for the Christian life.
Every preacher has his favored shorthand phrases and frameworks for the Christian life. When I was a member of Third Avenue Baptist in Louisville, some of us would poke fun at Greg Gilbert for how often he instinctively framed following Christ as a Tolkien-esque epic battle for faith. Of course spiritual battle is one prominent biblical paradigm, but there are many others. My point here is simply that some of those biblical paradigms are explicitly Trinitarian, and when you need shorthand for the whole Christian life you should use them.
The most obvious is adoption: the Father sent his Son to redeem us, and his Spirit to indwell us, in order that we would share in the Son’s own relation to the Father. The Christian life is not merely (and not ultimately!) about forgiveness and freedom from condemnation; it’s about being permanently inserted into the love and glory that the Father has eternally shared with the Son (John 17:5, 24, 26).
5. Use Trinitarian shorthand for the gospel.
Similarly, every preacher has his favored shorthand for the gospel. Here I would simply say, make sure that at least some of your gospel shorthand is explicitly Trinitarian. For instance, as Paul does in Galatians 4:4–7, you can build your gospel presentation out of the single, twofold mission of the Son and the Spirit from the Father. The Father sent his Son to redeem us from the curse of the law and sent the Spirit of his Son to indwell us and enable us to call on God as our own Father. There are many virtues of such a summary of the gospel. For one it is also a summary narration of Scripture’s storyline and a summary identification of the God of the gospel. Redemptive history and the two-testament canon that authoritatively attests that history turn on the Father’s sending of the Son and the Spirit. 
Such a summary of the gospel displays plainly that the Trinity and the gospel are bundled together. God revealed that he is the Trinity by sending us his Son and Spirit, and the salvation he worked for us has a Trinitarian shape and goal. If you mean to preach the gospel in every expositional sermon, and you should, then using Trinitarian gospel shorthand is a great way to make sure that not only the message you preach, but the God your sermon heralds, is truly and fully Christian.
 This is the thesis of Fred Sanders, The Triune God (Grand Rapids: Zondervan, 2016). The sentences that follow are also indebted to Sanders’s work.