This will be the first post that I’ve made specifically about the Trinity. Right now I’m not going to attempt to explain precisely what theologians mean when they talk about the doctrine of the Trinity.
The problem is, there just isn’t a single way to explain what the Trinity is; in other words, there is no “the” Trinity. There are many different approaches to explaining how the one God can simultaneously be the distinct persons of the Father, Son, and Holy Spirit. If you don’t believe me, just take a look at this Stanford Encyclopedia of Philosophy article on the Trinity. (Warning: That article can get very technical.) Nothing I’ve said so far should be controversial to you, as long as you are familiar with the literature on the subject.
Instead, I’m going to introduce a classic distinction between the economic Trinity and the essential Trinity. (The “essential” Trinity is also called the “immanent” or “ontological” Trinity.) In my view, this distinction is where all theorizing about God’s nature begins. No matter how you explain how God is (or is not) the Father, Son, and Holy Spirit, you assume the distinction I’m about to make for you.
The Economic Trinity
The lives of individuals are bound up with the economy of their nations. Those who were unfortunate enough to be working during the “Great Recession” (about 2007-2010) in the United States know what I’m talking about. What the U.S. government and its people did (or did not do) with its money affected the livelihoods of many Americans.
When I use the word “economy” here, what comes to mind for you? For me, it is what people do with the resources they have available. Obviously, most people use the word “economy” to refer to what people do with their money. But to refer to God’s “economy” has nothing to do with money.
However, God’s economy still refers to what he does with what he has available. And what does he have available? All points in time, events in human history, and all created things are under his control. In short, God’s economy (broadly) refers to what God does in his providential control of the world.
Now comes the narrow definition of God’s economy: it is how God acts in the redemption, or salvation of human beings. In other words, it is how God uses all of his resources to solve the problem of human sin and rebellion. It is what God does in human history.
The economic Trinity, then, simply refers to how human beings experience God in a threefold way in New Testament salvation. The New Testament makes it clear that the early disciples of Jesus experienced God in a threefold way. I simply don’t see how this point can be denied—even by Oneness Pentecostals—if you understand what I mean. The disciples walked with Jesus and learned from him during his ministry. They heard him talk about how he was sent by his Father. And when Jesus ascended into heaven they experienced Pentecost—where God poured the Holy Spirit upon them. That’s the threefold experience. That’s the economic Trinity.
But many, like myself, may not prefer to use the term “economic Trinity.” That’s because it assumes that God is the Trinity (notice I didn’t say “a” Trinity) in the first place. Because I will not assume Trinitarianism is true, I will instead refer to the “economic Trinity” as the “salvific triad” (or some variation). This gets the point across much more clearly when you are trying to have cross-denominational conversations.
A final note: Some want to also cash out the economic Trinity as how God acts during creation. In other words, they want to assign functions to the Father, Son, and Holy Spirit as distinct persons during creation. While I don’t think this is necessarily incorrect, I don’t think it is what primarily motivated the earliest Christians when they wrote the New Testament. I want to stick to my explanation—the experiential triad of salvation (or salvific triad)—because that is what they saw, and experienced, first.
The Essential Trinity
Now, how one explains how we experience God in a threefold way in salvation distinguishes one’s view of who God is in his nature from other views. Trinitarians, like Karl Rahner, argue that the economic Trinity just is (or is identical to) the essential Trinity. In other words, theologians like Rahner want to say that we experience God in a threefold way because he just is three persons.
Hopefully that gives you the picture, but let me state precisely what the “essential” Trinity is. In contrast to the economic Trinity (what God does), the essential Trinity is who God is in his essence (hence “essential”). Trinitarians want to say that God acts in a threefold way in human history because he is, in his very essence, tri-personal. He is three persons, and that explains why we experience him in a threefold way during New Testament salvation.
Obviously, this website wouldn’t exist if everybody agreed that the essential Trinity best explains the salvific triad. In the next post, I’m going to sketch an approach to classifying views of God based on the distinction I’ve made here. I will call the spectrum of views on God’s nature “theories (or views) about the Godhead.”
 Alister McGrath, Christian Theology: An Introduction, 5th ed. (Chichester: Wiley-Blackwell, 2011), 244.