I went to Wheaton College in Illinois, better known as Billy Graham's alma mater. Though part of the Evangelical subculture, Wheaton professors at that time were allowed a certain amount of latitude in their expression of the Christian faith. I had one Bible professor for instance who refused to affirm the Trinity. He said that he believed, as the Bible said, that the Father was God, the Son was God, the Holy Spirit was God and that there is one God. The Trinity, he said, was the church's working hypothesis of how those 4 statements could all be true.
And he is right. The word Trinity does not appear in the Bible, nor is the relationship of the three divine persons spelled out in a systematic way. But then the official definition of the Trinity, usually called the Athanasian Creed, doesn't actually explain it either. Rather it says what it isn't (three gods, or 1 god in 3 guises). What the church did in the definition of the Trinity is preserve the paradox by rejecting the ways people usually try to oversimplify the problem.
Why did people come up with the idea? Because they experienced God in 3 different ways. And even non-Christians have experienced God in at least 2 of these ways.
When most people think of God, they think of him as creator. They look at nature, at the universe, at their own bodies and think, “This isn't the result of an unimaginably long and unlikely series of accidents. Everything fits together too well. Some things have very clear purposes. God created this.” For most people God is the cause and the architect of all that is.
Some people sense God within themselves and/or within creation. Some religions see God as primarily an inner light or spark.
Christianity says, yes, God the Father is our creator and God the Holy Spirit works within us. But we also experience God in another way.
We affirm that Jesus Christ is God Incarnate. He is God become human, one of us. He knows from firsthand experience what our lives and our world is like. God is not remote or removed from us. He knows what it is like to suffer and even to die. As the saying goes, he's been there, done that.
But because he is God, in Jesus we see what God is like in terms we can understand, in terms of time and space and human personality, as J.B. Phillips put it. God is not an abstract force we can't relate to but a person with whom we can have a relationship.
And because we were made in God's image, and because Jesus is the image of God undistorted by sin, in Jesus we can also see what we were meant to be and can be if we let his Spirit work in us.
Jesus is the bridge between the Creator God above us and God within us, the Holy Spirit. Jesus is God beside us, so to speak. As the song says, “What if God was one of us?” The answer to that question is he'd be Jesus.
But how is it that we are not worshiping 3 gods? Or how do we know that God is not just appearing in 3 different modes or masks?
This is where 1 John 4:8 comes in. It says, “God is love.” It doesn't say God is loving, but that God is love itself. God is three divine persons in an eternal love relationship, so united as to be one. When we get married we try to achieve what it says in Genesis, that the two become one flesh or one organism. We humans fail to fully realize that but God is perfect love, perfect unity that does not mean the eradication of individuality.
I cannot explain the Trinity, not the way I can explain how an internal combustion engine works. But you know what? We can't even explain how a collection of neurons give rise to the awareness that I am a person. I think if we can't understand how human consciousness works we can hardly expect God to be easier to grasp. Surely God is an even bigger mystery than we are. If not, he wouldn't be God, but our creation.
What we can know is this: God created us, God lived and died as one of us to save us from our sins and rose to give us hope of new life, and God has come to dwell within us to guide us and make us into the people he always intended us to be. And we can know that God is love, the kind of expansive love that invites others into that divine relationship.
The best way to understand our Triune God is to experience him. Look upon his creation with awe and interact with it. Read and inwardly digest the accounts of his life as one of us. Absorb his teachings and appreciate his sacrifice for us. Open your heart and mind to his Spirit. Let him work within you to renew your mind and remake you into a new creation in Christ. And if you do, you will know the love that made us and that is the beating heart of all that is.