The only reason that the Church has to defend Trinity it was the Arius heretic point of view that Jesus is not God, and only created. At the end he had a tragic death in the toilet. He tried hard to fight Saint Athanasius on this matter. The Early Church they had Synodos when a matter was occured like the first recorded Synodos at Acts 15, when the Bishops had to discuss the matter of circumcission.
You need a lot to read regarding Trinity, in fact even my self I found it very hard to accept it. Also try to clean your head from the Arian heretic idea that WT and extereme Protestant groups hold. There are many passages in the Old Testament that shows the connection between the 3 persons. Even the Jesus said that you will baptized in the NAME of the Father the Son and the Holy Spirit.
So we have few questions here:
1. If the Father and the Son are persons why did Jesus didn't also separeted the Holy Spirit from the other 2?
2. Does a "force" has a name?
3. Why do Those 3 Father- Son- Holy Spirit share the same name YHWH?
This is just an example regarding Trinity. But I can give you the definition of Trinity in a very simple example and according to what the Apostolic Church set at at the 3rd century A.D.
The Sun has 3 elements:
1. The Star
2. Light
3. Heat
Those 3 elements they co-exist. But the cause of those elements is the Sun. So the Sun is the Father. Then we have the light. The Light(Jesus)comes from the Sun(Father)who is the Cause. And then the Heat(Holy Spirit) that again comes from the Source the Sun(Father)
Although those 3 elements are 3 seperate things they are one. Because they cannot exist apart. You cannot have the Light if you don't have the Sun, and again you cannot have heat without the Sun.
So the same with Trinity. The Father is the Cause of the Son and the Holy Spirit. Although they are 3 persons they are One. Father the Cause for the other 2 is higher than Jesus and Holy Spirit, because the Father is the Cause, that is why Jesus said the Father is greater than me.
The Trinity dogma is one of the basic differences between the Holy Catholic Apostolic Orthodox Church and the Papal Church(Catholic) Before the schisma the Symbol of Faith was set by the Church and it was accepted by the East and West Roman Church. After the Papal Church broke from the origninal dogma of the Church 1080 A.D they insert in the Symbol of faith that the Holy Spirit comes also from the Son, and this is on of the major points of disagreement.