The Son of God reveals who the Father is by being his
complement not his clone. Just as you know the bear by the imprint of his feet on the ground, so too you know the Father by the one who is the
imprint of his nature.
The Son completes the community of the Godhead by
being different (that's what being a complement means. A good wine complements a good meal - completes it, dare I say, it makes up for what is lacking. It doesn't mean that wine = better or that wine = more chips). The one is more sweetly enjoyed when accompanied by the difference of the other.
So we are left with the question who is the Spirit?
The Spirit is different again and completes the community of the Godhead by
consummating or unifying the complementary personalities of the Father and the Son as one. He flows eternally in love between the Father and the Son. He is the overflow of their delight in one another. To put it another way: Father and Son are one in the unity of the Spirit.
That sounds really abstract and weird so let's ground it. Remember, our guide is the Bible, and our interpreting principle is not western philosophical logic but the revelation of symmetry. (It's got to be really simple, otherwise we, along with some Indonesian tribes from the 14th century, will have an excuse for unbelief on the day of judgment.)
So here is my question: Where in the Bible, outside the trinity, is the only place where you see two united as one? Where do you see two complimentary persons united in loving, faithful, life-giving union? Where is this image, this metaphor of the divine nature, the divine life, clearly on display?
Marriage.
Which is exactly what you see in the creation of Adam and Eve. Two complementary persons unified as one in the bond of marriage.
I am personally absolutely convinced that this,
more than anything else, is what it means to be made in the image of God, (other interpretations e.g. "the attributes" tangent off into abstraction and speculation and encourage us to be self-obsessed and antisocial rather than generously outward-looking and sociable). This is simple biblical symmetry, that the simple-minded like you and me can understand. Wherever, you have biblical marriage, you have a simple, but profound picture of the divine life where beautiful diversity is found in perfect, faithful, life-giving unity. This is why Paul
cites sexual misconduct/dysfunction as the ultimate supression of the truth, because it stops us from seeing in real life, in concrete metaphor, (in glorious technicolour and surround sound - but don't let your mind wander too much there ;-) the divine life of God.
This is the reason you and I exist. It wasn't cos some single billy no mates god in the sky was bored one day and decided he would make a universe to trivially amuse himself. God is not a
sycophant desperate for human worship. When a husband and wife, express the greatest joy and delight in each other a delight that is exclusive, faithful, physical, mental and spiritual - in short all-consumming (or consummating) - the overflow of that delight is life in the form of a child. In this way, they echo the Father and Son, who in the power, joy and faithful union of the Spirit overflowed in creative pleasure and made the whole cosmos, both seen and unseen. The marriage bed, is a theatre of the intimate, invisible life of God and should be
respected by all. Oh how I need help to feel the weight and beauty of this and fight my tendency to reduce sex to a merely mechanistic/selfish act of gratification.
Only the triune - diverse, yet unified - God of the Bible can truly
be love: self-giving, life-creating love.
The reason we call God: Father, Son and Holy Spirit and not Man, Woman and Holy Matrimony is because the story doesn't finish at creation, (in fact, it doesn't begin there either) but at salvation and re-creation. The symmetry of marriage is not just a means of understanding the Trinity, but also the relationship Christ has with the church. But that is for another post. We haven't reached the
bottom of the rabbit hole just yet!
tbc...