This article is a reflection on why most Bible-oriented Christians have such a difficult time considering Unitarianism to be an option, and how to address the barriers that prevent them from doing so.
Most Christians who take their religious life seriously are not very concerned with the details of the doctrine of the Trinity. Many essentially maintain a very vague idea of what the doctrine is supposed to mean, cannot give any formal or particular descriptions of it, and could not defend it in a debate. If given time, they may come up with something like the seven-claim Trinity model, but would not be able to articulate much beyond that.
However, what most of them who think about theology are concerned with is the Deity of Christ. They have become very convinced that the Bible teaches that Jesus is God. At the same time, they believe that the Father is God, and also that Jesus is not the Father. How exactly those 3 facts fit together is almost always an issue of secondary importance to them. Far more important is that, no matter what, the Deity of Christ must be maintained, because defending the doctrine has become synonymous in their mind with defending the Bible, and their religion.
This confidence in the Deity of Christ is why they remain Trinitarian. Most of them who give the doctrine of the Trinity a brief study are not very pleased with its complexity, and would probably relinquish it if they thought it was possible to remain Christian and do so. But, in their mind, they cannot relinquish it, but instead are bound to it, because the Deity of Christ, to them, is absolutely certain. So, even though it may confuse them, they bear with it, because they believe that it is their only recourse to working out the teaching of the Bible regarding God and Jesus.
Typically, when a person holds to a doctrine that they believe comes from the Bible, they will have a core set of texts which they appeal to as teaching that doctrine explicitly. With regard to the doctrine of the Deity of Christ, for most believers, there will be a core set of about 4 or 5 passages (Isaiah 9:6, Matthew 28:19, John 1:1-14, John 20:28, Hebrews 1:8-12, for instance) which they would regard as a foundation, where they believe that the doctrine is very clearly taught. There may be scores of other texts which they would accept as being "indications" or "supporting" the doctrine, but ultimately, these are texts which they are basing their foundation upon.
Getting them to reconsider the meaning of these verses is very difficult. Even if they become persuaded that a Unitarian interpretation of a particular passage is possible, it will likely still be rejected, because they have already been persuaded of the Trinitarian view of it, and that has become part of their theological framework, which is not easily dislodged.
Ultimately, I believe that there are two big factors which will determine whether a person will be willing to reconsider their proof texts, and therefore the Deity of Christ or the Trinity:
If someone cultivates knowledge of the Trinity, then it will crystallize in their mind the potential problems created by their belief in the Deity of Christ. The Trinity is first and foremost an attempt to reconcile the conclusion that Jesus is God with the facts that the Father is God, the Father is not Jesus, and that there is one God. When they learn of the tremendous complexity involved in this undertaking, they will be far more likely to reconsider their initial conclusion that Jesus is taught to be God in the Bible, and will also be informed enough to recognize what would be valid critiques of their position.
I firmly believe that if every professing Trinitarian was fully educated on what their churches teach on the specifics of the doctrine - to the point where they would be able to defend it in a debate, for instance - then I believe that most people would eventually relinquish it. There would be dogmatic defenders, who are the type of people who would have created the doctrine in the first place - but the average person? I believe they would not put up with its many appeals to mystery, or apparent contradictions, or the fact that many of the means of attempting to reconcile the doctrine are not taught in any passage of Scripture.
With regard to taking a big-picture view of this issue in particular, I mean that one should move beyond proof-texting, and begin to consider questions like:
Once someone's mind can be set on considering questions like the above, they are well on their way to leaving Trinitarianism. Once they have been encouraged to take a few steps back, and look at things from a big-picture perspective, then they will begin to be rid of whatever tunnel vision is produced by staying in a few favorite texts, and ignoring the great body of evidence against the doctrine.
We cannot, as Unitarians, make someone study the doctrine of the Trinity deeply. We can, however, be informed on various Trinity theories, and attempt to inform the people we engage with of what they teach on various issues, and what their respective weaknesses are. Then, keeping the argument at a big-picture level is simply a matter of preparing a few good examples to be able to go through and explain the questions above, which invite one to survey the entire New Testament's teaching about God.
Getting someone to consider a Unitarian perspective of God and Scripture is a combination of getting them to understand the difficulties which arise as a result of concluding that Jesus is God, and also, showing them that the New Testament can be viewed in a Unitarian way, and that belief in the Deity of Christ is not synonymous with a belief in the Bible. So, our goal as Unitarians should be to inform them on the difficulties involved in whatever Trinity theory they hold to, along with constantly encouraging them to step back, and consider the New Testament from a big-picture perspective.