I believe that the doctrine developed along strictly theological lines over centuries, slowly at first but never rashly.
I believe that it is the most rational way to reconcile all the factors that the Bible reveals about The Father, Christ, and the Holy Spirit, without doing an injustice to the text by diminishing the substance of what it says in all its revelation.
The Father is God
Christ is revealed in Scripture as God
But He is not the Father
He is subordinate to the Father but not inferior to Him
Being fully God He was also in all respects human but sinless
The Holy Spirit is revealed in Scripture as God
There is only One God
All these statements are revealed truth, but not explicable truth. Because this not so easy to understand, or believe, I feel that that the Bible, and God, has left each one of us as responsible for the expression of our own faith. We will ultimately stand or fall on the basis of our belief.
We can quite easily say: "I don't understand it so stuff it"
Or, "I don't understand it so I'll make it understandable"
Or we can say: "I'm not required to understand, only believe. So I believe"
I will never say that, because I believe therefore you must. It is not my place to determine another individual's belief. It is important that each person embark on his/her own spiritual journey, walking in his/her own shoes. The goal may never be reached, but the quest is what life is about. It is what extends the very meaning of being part of the human species.
Cheers