Why should we believe in the Trinity... and does it matter?

Recently we turned our minds to two big questions

1. Why should we believe in the doctrine of the Trinity?
2. Why does it matter... what is the 'cash-value' of holding to such a doctrine?

So... why should we believe that God is Trinity... 1 God - 3 persons?

The question of the Trinity really arises out of the impact of the person of Jesus.

The New Testament teaches unequivocally that Jesus Christ is divine. For instance listen to the testimony of the apostle John...

• John 1:1 "In the beginning was the Word and the Word was with God, and the Word was God." That is, Jesus is the preexistent Word... both God and with God. Jesus is the incarnation of the preexistent God
  
• John 1:18 "No one has ever seen God; the only God who is at the Father's side, he has made him known."
  
• And then in John 20:28, Thomas turns to the resurrected Lord Jesus and declares, "My Lord and my God." A statement that Jesus commends Thomas for rather than rebuking him.
  

So that's the first step in the argument that leads to the Trinity... the New Testament teaches that Jesus is God.

The second step is the universal witness of the Scriptures that there is only 1 God. For instance listen to the prophet Isaiah...

• Isaiah 43:10 "Before me no god was formed, nor shall there be any after me."
  
• Isaiah 44:6 "I am the the first and I am the last; beside me there is no god."
  
• Isaiah 45:5 "I am Yahweh, and there is no other, besides me there is no god..."

The conundrum for the early Christians was how they hold those two things together. Jesus is God... AND... there is only one God. No wonder it took them the better part of 3 centuries to confidently affirm a solution.

There are several options:

1. Modalism teaches that there is one God who takes 3 successive forms. God is Yahweh the Father in the Old Testament, then he become Jesus Christ, and now God is the Holy Spirit. There are any number of problems with that. For instance, how does it account for the fact that Jesus was preexistent? How does it account for the command to baptise in the name of the Father, Son and Spirit?
   
2. Adoptionism teaches that Jesus was a good man whom God adopted as his Son. Once again, it does not explain the teaching about Jesus preexistence.
   
3. Arianism teaches that Jesus is the first and greatest creature created by God. However, that does not take seriously the teaching of the New Testament that Jesus is not just god-like, but that he is God.
   
4. Tritheism argues that the apparent monotheism of the New Testament was not the full picture. There are, in fact, 3 Gods. While it is true that many of the New Testament passages could be read in a way consistent with tritheism, to discount the clear teaching of the bible that there is still only 1 God is not an option open to bible believing Christians.
   
5. Trinitarianism is therefore the only biblically possible solution to the conundrum. There is one God who exists as 3 persons (of course, this is to assume the distinct personality of the Spirit - which is another issue altogether). With 20-20 theological hindsight it is then clear that the way that Jesus speaks in a passage like John 14:1-11 assumes the Trinity.
   

So, why does it matter? What is the 'cash-value' in believing that God is Trinity?

There are countless profound and practical way in which this sort of thinking pays off. Here are two:

1. It shows that at the heart of the universe is not an aloof detached God like the Allah of Islam. Instead reality at its most real is an eternal set of relationships. That is, relationship is at the heart of the universe! And because God is relationship it is possible for him to genuinely include us in that relationship.
   
2. Unless we hold that the way God reveals himself in Jesus is not true to who he is in himself, then the doctrine of the Trinity shows us that it is specifically other-person-centered relationships that are at the heart of the universe. The Son eternally submits to the loving will of the Father. The self-effacing Spirit is eternally directing us to the Father and the Son. This means that loving leadership, willing submission and humble service are the most supreme realities in the cosmos. For us to be made in God's image means that we are made for other-person centered relationships of love, submission and service.
   

Any more suggestions for ways in which believing the doctrine of the Trinity ought to make a practical impact?