Is the Trinity biblical?

Certainly.  

As is Unitarianism, Oneness Pentecostalism and every other denomination under the sun. 

Those who developed the doctrine were highly intelligent (arguably too intelligent perhaps), it was not invented during the Council of Nicaea, it finds it origins in the earliest strata of the Church (though non-Trinitarians claim the same) and it is most certainly rooted in Scripture as the primary source (as any and all who call themselves Christian in some fashion or other claim). 

Are Oneness Pentecostals biblical? Unitarians? Christadelphians? Worldwide Church of God? Jehovah’s Witnesses? 

In other words, whether one agrees with it or not, the Trinity is biblical. 

A better framing of the question might be: in what way does the Trinity doctrine find roots in the Bible?

There is a lot of discussion, online anyhow, about doctrine. Volumes and volumes of books are published on the same subject. I don't know how much this applies in the day to day lives of most who call themselves Christians.

But it dawned on me as I continue my journey into Orthodoxy that I see why people criticize the Orthodox Church (though often lumped in with Catholicism). It is one of the oldest expressions of the faith for certain. Yet in its current form it really dates to the 4th century.

This isn't to deny that it may be traceable back to the Apostles and that the worship the developed in the 4th century reflects truly the earliest church.  But I get it. With the complex doctrines and the formality and 'ritual' that is the church by going Sola Scriptura (understood in a way different than Luther's original intent) the current church only looks for roots in the Bible.

The irony, if I am using that word properly, is a written reflection of the tradition that was passed on and the same church that is criticized is the same church who canonized what we call the New Testament and who also developed doctrine.

Next step, after cutting themselves off from the larger body of the church, is to do some self-reflection and reject the doctrines of the church. This is already happening today. Doctrines are given lip service and half-hearted apologetic but changes are happening on a large scale. 

Oneness Pentecostals, for example, are a growing body of believers who reject the Trinity. There are some who are seeking to do away with the part in the Creed about Jesus going to hell. It's being dismantled, slowly but surely. What will be left? Hard to say.

But all of them go back to the Bible as their source.

So is the Trinity biblical? It most certainly is.

I think what appeals to be about Orthodoxy is twofold:

1) Its embrace of the mystery

This does not mean throw up your hands because it is not understood. It means that doctrine is a hedge, it is a limit. Over hundreds (yes, hundreds, longer than the United States is a country) of years it has been unpacked, all the mental and intellectual limits of how to understand what has been presented in the text we now have we call 'the Bible', and the Trinity is what resulted. However, within (and this is the operative word) those limits is an unfathomable richness. It is this that is mysterious. Doctrine (the Trinity and the God-Man) is both the end and the entry into the divine.

I have found that the end result of all questioning yields to the Trinity.

2) Its doctrinal framework.

It makes sense. It makes sense of the disparate elements between all the books of the New Testament in their presentation of Jesus as well as the Father, Son and Spirit. Certainly there's belief involved. After all, Three-In-One sounds absurd, especially when contrasted with the Judaism out of which it arose.

In the eastern tradition it wasn't until the 7th century that everything was 'settled'. And yet over time there is still more to discover, more nuances, more exploration into what it means. It never really ceased.

And this is where 'new' revelations come in such as Oneness Pentecostals. They say they have it right, that 2,000 years of church history was a power grab. God is speaking afresh and new. Revival! The end times! Jesus is coming soon! It's certainly an interesting time to be alive.

And yet, all are biblical.

My point of all this? Pick one and go with it. Seek to live it, not debate about it.

Nesotrius Was Not Nestorian, Was Arius And Arian?

The deeper I dig in to this stuff, it seems as if many of these 'heretics' were but props, 'types' against which doctrine was defined and in the politics of the times I'd imagine persecutions over the years off and on put this in context in which we have little understanding as to the machinations used to ensure 'true' doctrine was entrenched.

I think we're seeing this played out on a different scale today when one person's text, tweet, whatever, is taken out of context (there is no time for context in our instant world) and blown to extremes whether or not the meaning is what it is said to have meant.

The logical extension of the 'worst' of Antiochene thought led to the accusations Cyril railed against Nestorius; it didn't necessarily matter whether or not he actually believed what was said. Ditto what was said about Cyril.

It is probably the same way with Arius. What is left of Arius' beliefs is found primarily in Athanasius. Not exactly an unbiased source of information. 

They became props against which doctrine was delineated and defined.

We do the same thing today with the various denominations when in reality we seem to have lost what the 'Trinity' actually means. Truthfully, when I read the Oneness arguments I think they are trying to say the same thing about the mystery. There are differences, obviously, such as the fact that the pre-existent 'Jesus' was in the mind of God and not a pre-existing Word that became man. Significant difference, certainly, from 'orthodox' thinking but in truth, when we drill down, we are trying to take the Biblical witness and put words to the mystery.

I will revisit this but I believe as Christians we are more united than we are divided and we spent more time infighting than we do trying to show people the beauty of the Christian faith.

I became a Christian spontaneously and it took me almost 20 years to want to be one.