Or you can know them personally: what their passions are, what makes them tick, what that funny look they sometimes get on their face means, without them having to tell you. You can know a lot about a person in that first way, without ever coming to know them in this second way.
Theologians sometimes differentiate between two different ways of understanding the Trinity, too. We can use the Trinity as a way of describing what God is like in his inner life, or we can use the Trinity to describe how God relates to us in a personal way.
The word “ontological” describes this first way of understanding the Trinity. “Ontological” means “having to do with one’s essence or being,” and the “Ontological Trinity” is a way of trying to describe what you might see if you could open a window on heaven and peak into God’s throne-room: God as God is in and of God’s-self.
The phrase “economic Trinity” describes this second way of understanding the Trinity. The “economic Trinity” is a way of describing how God is at work and has been at work in history—in creation, in world history and in our own personal lives: God in relationship with us.
Think about it like this: as the Son of God, Jesus taught his followers to pray to God as “our Father in Heaven”; and if we take him at his word and do pray like this, it’s only because the Holy Spirit has confirmed the truth of Jesus’ words in our hearts.
In other words, we come to know God as the Father, through the Son, by the Holy Spirit.
The story of Jesus’ baptism shows us the same thing from a slightly different angle. John the Baptist baptizes Jesus and then it says, as he was coming up out of the water, the Spirit came upon him in the form of a dove and a voice from heaven said, “This is my Beloved Son in whom I am well pleased.”
Again: God reveals himself as Father, through the Son, by the Holy Spirit.
Our relationship with God has this same Trinitarian “shape” going the other direction.
Take prayer, for instance. Often when people pray they feel alone and kind of inadequate, like their words are just bouncing off the ceiling.
Yet the Bible teaches that when Christians pray, the Holy Spirit actually puts the prayer of Jesus in our hearts, who mediates for us as our Great High Priest, bringing our prayers before the Father in Heaven.
It’s never just us praying to God on our own. We pray to the Father, through the Son, by the Holy Spirit.
Or take our worship. Because we’re flesh-and-blood human beings, we never really give God the love, honor and glory he deserves; yet Jesus, who was fully God and fully human, poured out his sinless life, as a perfect act of worship on our behalf. And when we believe in Jesus, the Holy Spirit unites our lives with his life, so that our worship, as imperfect as it is, is offered with his perfect worship: to the Father, through the Son, by the Holy Spirit.
A lot of Christians don’t get especially excited about the Church’s teaching about the Trinity, because they tend to think of it in terms of that first way of knowing God: cold, objective facts about what God is like, in and of himself; and they don’t think about it in this second way, as the very bedrock for our whole relationship with God.
But that’s what it is. It’s how we know God—how we’re able to know God—and it’s how we live with God. For a Christian—prayer, worship, ministry, service, discipleship—all of it is only possible because we know God, as Father through the Son by the Holy Spirit.