Why do we believe God is a Trinity? - Acts 2:14-36

Then Peter stood up with the Eleven, raised his voice and addressed the crowd: “Fellow Jews and all of
you who live in Jerusalem, let me explain this to you; listen carefully to what I say. These people are not drunk, as you suppose. It’s only nine in the morning! No, this is what was spoken by the prophet Joel:

“‘In the last days, God says,
    I will pour out my Spirit on all people.
Your sons and daughters will prophesy,
    your young men will see visions,
    your old men will dream dreams.
 Even on my servants, both men and women,
    I will pour out my Spirit in those days,
    and they will prophesy.
 I will show wonders in the heavens above
    and signs on the earth below,
    blood and fire and billows of smoke.
 The sun will be turned to darkness
    and the moon to blood
    before the coming of the great and glorious day of the Lord.
 And everyone who calls
    on the name of the Lord will be saved.’ (Joel 2)

“Fellow Israelites, listen to this: Jesus of Nazareth was a man accredited by God to you by miracles, wonders and signs, which God did among you through him, as you yourselves know. This man was handed over to you by God’s deliberate plan and foreknowledge; and you, with the help of wicked men, put him to death by nailing him to the cross. But God raised him from the dead, freeing him from the agony of death, because it was impossible for death to keep its hold on him. David said about him:

“‘I saw the Lord always before me.
    Because he is at my right hand,
    I will not be shaken.
 Therefore my heart is glad and my tongue rejoices;
    my body also will rest in hope,
 because you will not abandon me to the realm of the dead,
    you will not let your holy one see decay.
 You have made known to me the paths of life;
    you will fill me with joy in your presence.’ (Psalm 16)

“Fellow Israelites, I can tell you confidently that the patriarch David died and was buried, and his tomb is here to this day. But he was a prophet and knew that God had promised him on oath that he would place one of his descendants on his throne. Seeing what was to come, he spoke of the resurrection of the Messiah, that he was not abandoned to the realm of the dead, nor did his body see decay. God has raised this Jesus to life, and we are all witnesses of it. Exalted to the right hand of God, he has received from the Father the promised Holy Spirit and has poured out what you now see and hear. For David did not ascend to heaven, and yet he said,

“‘The Lord said to my Lord:
    “Sit at my right hand
until I make your enemies
    a footstool for your feet.”’ (Psalm 110)

“Therefore let all Israel be assured of this: God has made this Jesus, whom you crucified, both Lord and Messiah.”

Today is Trinity Sunday and our reading follows on directly from the reading for Pentecost we had last week. Last week we heard about the first Pentecost, when the Holy Spirit was poured out on the Jesus' disciples and they were blessed, praising God in many languages. In response to this a crowd gathers around them wondering what is happening, and Peter addresses them as we have heard. This is perhaps the first Christian sermon, and it is rather humbling to be following in its steps today.

It is also a great reading for Trinity Sunday, because here he talks about all three persons of the Trinity: God the Father, Jesus the Son and the Holy Spirit being present and active in the events of Easter and Pentecost, and through the three persons of God we are carried up and included in God's great work, with the Spirit within us, the Son beside us, and the Father above us. Humanity is the 4th part of this, called to be part of Christ's body, and so surrounded by God.

In the Gospels, the disciples often struggle to grasp what Jesus is telling them will happen, but here after time with the resurrected Jesus following Easter, and with the Holy Spirit newly come upon them they finally understand God's plan to build his Kingdom. Here we see the very earliest Christian theology, the attempt to wrestle with the astonishing things that the Disciples had seen. And the understanding of God as a Trinity of persons is at the very centre of that from the beginning.

People sometimes struggle to understand the idea of the Trinity, and they use all kinds of odd analogies to compare God to things in our world. But while we should try to understand this idea, we must remember that we will never fully grasp the nature of God with our mortal, limited minds. But thanks to God revealing himself to us we can get a partial view of his eternal nature "as in a cloudy mirror" .

This is profound and fundamental stuff, and we should not expect it to be entirely simple, just as the world we live in, the universe we live in, can be complex and paradoxical. The more Science delves into the fundamental nature of physical reality, the more astonishing it seems to be. When I was at university, we studied Einstein's theory of Relativity: did you know that if you travel fast enough, time actually slows down, from your perspective, but not that of the people around you? Did you know that gravity also actually slows down time by distorting the fabric of space around massive objects? Did you know that at very small sizes, quantum sizes, physical matter acts like a wave and can diffract and refract the way lights does when it shines through water? Did you know that mathematicians study different sizes of infinity, and that if you add one infinity to another, it's the same size, but if you take an exponential - say two to the power of an infinity, you get a larger infinity?

Now, you may wonder why I'm getting off the topic, but I promise you all this is relevant, because, as C.S.Lewis once said, we should not expect spiritual reality to be any less complex and bizarre than physical reality; we should not expect Theology to be less wonderful than Physics. Indeed, it is from that spiritual reality, it is from God, that the complexity and beauty of the physical world originates. "The heavens declare the Glory of God, and the skies display his handiwork", as the Psalms say.

And when we are talking about the Trinity, we are talking about the Special Relativity, or the Quantum Mechanics of Theology. There's lots of things about God, lots of true things, that even a small child can understand; just like there's lots of things about the natural world, about the Sun and Moon and stars, that anyone can grasp. But with the Trinity you're getting into the heart of things, the fundamental reality that everything else comes from: and that is going to start stretching us.

So why do we describe God as a Trinity? Well, because it is the only explanation that fits the evidence. In Physics, Special Relativity and Quantum Mechanics were nobody's first guess. Nobody invented them because they seemed sensible or common sense, or because they're what you come up with if you just sit down and try to be reasonable about it. No. They are complex, counter-intuitive ideas that are demanded by the facts we have gathered through experiments.

In the same way, the Trinity is nobody's first idea of what God is like, it's not common-sense, it's not the sort of theory you come up with if you just sat down and made something up. But it is beautiful, and it is the truth. It is the understanding the Apostles, and the generations of Christians who came after them, put together because it seemed the only one that fit the facts they had experienced. So, what sort of facts are those?  When we seek to understand physical reality, we get laboratories and telescopes and a lot of equipment, but we can't do that with Spiritual reality. God is not an object to be measured and weighed, but he is a person, three persons in fact, and because we are persons too, made in God's image, we can experience him because he has revealed himself to us. This is the type of evidence that we have, it is the kind of evidence you have that someone loves you, it is the kind of evidence you have that music is beautiful; or that life is worth living: it's the experience of the heart, the spirit and the soul, of one person revealing themselves to another. It is the type of evidence that, in the end, really matters.

So what facts led to the understanding of the Trinity: that the one God, the creator of all things, exists in three persons, as Father, Son and Holy Spirit? Firstly, was the experience the Apostles had of Jesus himself, that here was a man who spoke of God as Father, as separate from him; but who also did miracles, forgave sins on his own authority, commanded the wind and waves to obey him, who fulfilled the prophecies about God coming to his people, and revealed God's Kingdom as though he knew its every detail. Here was a man who described himself as the Son of the Father, who alone reveals the Father - The Way, The Truth and the Life. And they had witnessed the Father honouring Jesus as his Son, most gloriously through his Resurrection. This was a man, but this was not just a man, this was Emmanuel - God-With-Us.

So there was God, who Jesus had revealed to the apostles as the Father, and then there was Jesus his Son, two persons of God: but there was also a third. There was the Holy Spirit that had been poured out onto them, whose power they felt moving within them, speaking to them. This was not the Father, for the Father exists infinite and eternal, beyond time and space and our physical universe; and it was not the Son, it was not Jesus, who they had seen ascend into heaven; it was a third person of God that they were all experiencing resting in them, filling them with courage and understanding. This is the reality that generation after generation of Christians have lived with, through struggles and triumphs and losses; and the reality we can only explain through the idea of the Trinity: the Father who created all things; the Son who walked on our earth and lived our life and bore our hurt; and the Spirit who dwells every day within us.

It is important to realise that this is not just a New Testament idea, either. God did not become Trinity when Jesus was born, or baptised, or resurrected. God has always been Trinity, from eternity to eternity, and that is written throughout the Bible, from beginning to end. It is easy for us to look for the Trinity in the New Testament, but as well as their own experiences, the Apostles and early Christians looked into the only Scriptures they had: the Hebrew Scriptures, that we call the Old Testament. And we can see that in the reading today: Peter makes clear what the Father has done through Jesus at that time, but to explain this to the people of Jerusalem, Peter looks back to the Old Testament scriptures they knew so well.

Firstly, he claims the promise of the Prophet Joel that God, "will pour out [his] Spirit on all people", that "sons and daughters will prophesy" and "even on my servants, both men and women, I will pour out my Spirit". Then he quotes from the Psalms: notice here that Peter is saying it is Christ himself speaking in that first psalm. When it says "I saw the Lord always before me, because he is at my right hand", that is Christ, the Son, talking about his Father, though David wrote the psalm. We know this because he refers to himself as the "holy one" who will not be abandoned "to the realm of the dead", but as all Jews knew, David sinned, and he died, and his tomb was known. It is Christ who was resurrected. Then in the second psalm it is not Christ speaking, but David being given a glimpse of the Father addressing the Son: "The Lord said to my Lord, sit at my right hand". David was the King of Israel, he had no Lord except God, so who are these two figures: The Lord addressing David's Lord? They are the Father and the Son.

The New Testament is not some dramatic left-turn away from the path taken by the Old Testament, rather it is a reflection on a thousand years of God's promises to his people; and whether it's the Gospel, or here in Acts, or Paul's Letters, it declares with one voice that the Hebrew Scriptures, the Old Testament, spoke of Christ. This is one of those things that sounds strange at first, but when you know where to look, you start seeing it everywhere. Now, when I say the Old Testament speaks of Christ, that could mean two things: firstly, it could mean the Old Testament prophesied and promised that Christ would come. It certainly does that, if you've ever listened to a 'Nine Lesson and Carols' service at Christmas-time you have heard a highlight of points in the Old Testament when Christ's coming was promised; or you can read Isaiah chapter 53, the Suffering Servant, and I really challenge you to tell me that passage isn't describing Jesus, though it was written 500 years before he was born.

So the Old Testament promised that Christ would come: as Emmanuel, God-With-Us, and Jesus fulfilled those prophecies. But, just as important for understanding why we have our doctrine of the Trinity, is the fact that God the Son, who has existed from eternity, and was born in Bethlehem as Jesus, Mary's Son; also appears in the Old Testament, again and again. He appears, as a separate person from God the Father; and he is recognised as God, by people in the Old Testament. In the same Old Testament that famous declares that "the LORD is our God, the LORD is one", the same Old Testament that is the source of Monotheism, our belief in One God, that we share with Jews and Muslims, and Sikhs and others.

In the Old Testament, the Son appears most often as a mysterious figure identified as the 'Angel of the Lord'. Do not be fooled by the word 'angel' though, for this is no mere angel, but rather one who is sent by God to save and teach his people, who speaks as God, and is recognised as God. If I were to go through all the times this happened, I would be here all day, so I just want to briefly talk about two of the first examples in the Old Testament from the book of Genesis.

Hagar was the maidservant of Sarah, the wife of Abraham, but because Abraham and Sarah had no children, Abraham took Hagar as his wife as well, and Hagar became pregnant with a son. But Sarah then was jealous of Hagar and so mistreated her, leading to Hagar running away into the wilderness. There the Angel of the Lord found her in the wilderness and told her to go back, and promised her that God will bless her son and make him the father of a great nation. This is how she responds (in Genesis 16:13) - "She gave this name to the Lord who spoke to her: “You are the God who sees me,” for she said, “I have now seen the One who sees me.”" Hagar has spoken to the Angel of the Lord, but she knows she has seen God. Who is this God, who comes as the messenger from God?

Then two generations later we have Jacob, Abraham's grandson, and he had run away from his family because he was afraid of his brother Esau. Now years later he is returning to his family with his wives and children, afraid that Esau will attack him. The night beforehand though, he has a strange meeting: a man appears from nowhere and wrestles, physically grapples with Jacob through the night, until morning is about to come, then the man touches Jacob's hip and dislocates it. The man then says to Jacob "“Your name will no longer be Jacob, but Israel, because you have struggled with God and with man and have overcome.”", he blesses Jacob and then disappears. Jacob is in no doubt about who he met, like Hagar he says (in Genesis 32:30) "So Jacob called the place Peniel, saying, “It is because I saw God face to face, and yet my life was spared.”

I could quite literally go on and on like this for some time, there are so many examples, and when you realise what you're looking at, they're so clear. John's Gospel tells us that "nobody has seen the Father", except the Son. So who is this God, who comes from God the Father, who meets us face to face, who brings God's blessing to Hagar, and to Jacob, and so many others throughout the Old Testament? He is the Son, who in the fulness of time was born in Bethlehem at the first Christmas, and ever since we know as our Lord Jesus Christ, who unites our humanity with God forevermore. But God has always been Trinity from the beginning. That is what Peter is talking about in our reading today, that was what Jesus meant when he claimed that the Law and the Prophets all pointed to him, and that has been the Christian faith from the beginning.

Why does this matter though? Until we see God face-to-face in heaven none of us can fully comprehend how the three persons of the Trinity relate to each other, or how they share a Will and Purpose as One God. But this is not just a matter of abstract theology, it matters because it is at the core of what God has done for us. God became one of us and died for us; God's Holy Spirit dwells within us. That is amazing, and if we did not believe God is Father, Son and Holy Spirit, we could not say it was true. It was not some prophet or spirit somewhere between us and God who became man and died for us, it was God himself. It is not some mere blessing from a distant God that lies upon us, it is the Holy Spirit, God himself, who lives within us. It is this that makes the Christian faith unique.

Islam, the Muslim faith, is in many ways like Christianity, it is based on belief in One God, that is believed to be the same God described in the Old Testament. But it differs from Christianity in this one crucial point: Muslims believe that it is not possible that God could have been born as a man and died for us. Islam believes that to stoop so low, as to be born in a stable, and to die on a cross, would shame God, would make God less.

We believe that it makes God more. We believe that God is so glorious that by being born as a Man he makes humanity and our whole world holy. We believe that it proves God is even greater than we imagined, that he could face death on the cross and make it no shame. We believe God showed greater love than we could imagine, because he did not scorn our weakness. We believe that the martyr who sacrifices his own life triumphs nonetheless, because the Holy Spirit within him is more powerful than any physical force or violence. It is this faith that allows Peter, in our reading today, to speak with such astonishing confidence, as he does again and again in Acts, knowing that the power of mobs and armies and kings is nothing before the power of Jesus Christ.

Christ changes everything, he changes lives, and whole societies; he is the sure and certain rock around which everything else in this world must turn, because he is God. Through the Holy Spirit there is nothing we need fear, for the power within us is greater and more enduring than any in the world, because he is God. And all this comes from the Father, who is the eternal source and creator of all things. 

And for that, Amen!