I responded to a similar question today. I'll just repost it here.
I'm a non-Trinitarian. I certainly don't worship three Gods.
I personally believe that the majority of Christians are actually Oneness in their view of God, but accept the Trinitarian explanation because it's the dominant view. That's why we so often hear "I believe in the Trinity, but I don't understand it."
I think the doctrine of the Trinity is a logical impossibility. God cannot be Three and One.
There is no evidence that any of the writers of the Old or New Testament believed in the Trinity, and the historical record shows that the doctrine developed over a period of 250 years, from 150AD to 400AD.
My understanding of the Oneness of God is really simple. God is not limited in how He can manifest himself in the world.
He's the Father because he created the universe, and He's the Father of the man Christ Jesus in a unique way, because of the incarnation.
The term Holy Spirit refers to God. God is a spirit, and God is holy. The term is always used to describe the God actively doing something. Here's the first mention of the Spirit:
The earth was without form, and void; and darkness was on the face of the deep. And the Spirit of God was hovering over the face of the waters. Then God said, “Let there be light”; and there was light. (Ge. 1:2-3)
For thousands of years, no one interpreted that verse in anything but a strictly monotheistic sense.
The most incredible thing that has ever happened in the history of the world is this: God Himself took on the mortal form of a man and lived a sinless human life, obedient even unto death.
And without controversy great is the mystery of godliness: God was manifested in the flesh, justified in the Spirit, seen by angels, preached among the Gentiles, believed on in the world, received up in glory. (1Tim 3.16)
The mystery is that Jesus Christ could be completely human and completely God at the same time. That is a mystery!
But if you think about it, the doctrine of the Trinity doesn't make this mystery any easier to understand. Whether one of the three "co-equal, co-eternal Persons" of the Godhead dwelt in Jesus, or the one and only Spirit of God, you still have the same mystery. How could he be God and a human? Why did He need to pray, or for that matter to eat or sleep, if God is omnipotent? Did God suffer? The same questions have to be asked about a Trinitarian God and a Oneness God.
If you know anything about the rules of logic, you're familiar with the concept known as Occam's razor. It basically says this: if you have more than one hypothesis that explains the same results, the hypothesis that requires the fewest assumptions is the best.
The Oneness view requires us to believe that God can manifest in many different ways, and can even manifest in more than one way at the same place and time (for example, at the baptism of Jesus: God was manifested as the voice from heaven, the Holy Spirit descending as a dove, and the man Jesus Christ).
The Trinity view requires us to believe that God can manifest in many different ways, but has been divided in three distinct personae for all eternity. That's a much bigger assumption, and it's not directly supported by any New or Old Testament scripture, and it at least seems to contradict the single most important doctrine of the Old Testament:
“Hear, O Israel: The LORD our God, the LORD is one!" (De. 6.4)
I'll just put one brief explanation here. The "Word" in John 1. Since the 200s A.D. at least, some have used this chapter to argue for the preexistence of Jesus (before the Incarnation). I don't think it's necessary to believe that. The word of God is God's plan for the world, and for humanity. The Greek word used in John 1 is logos. The same term was used in the Greek translations of the Old Testament throughout the Psalms:
By the word of the LORD the heavens were made, and all the host of them by the breath of His mouth. (Ps. 33.6)
and throughout the New Testament, for example:
For the word of God is living and powerful, and sharper than any two-edged sword, piercing even to the division of soul and spirit, and of joints and marrow, and is a discerner of the thoughts and intents of the heart. (He. 4.12)
These verses don't seem to be referring to an eternal Son. If we accept that John 1 is referring to an eternal Son, we should also expect that every other reference, in the Old Testament and the New, to the "word of God" is also referring to the Son, and that's just confusing.
TL;DR--The doctrine of the Trinity doesn't make it any easier to understand the Incarnation of Jesus Christ. It at least seems to contradict the strict monotheism of Judaism. It requires us to believe a doctrine about the eternal nature of God that is not explicitly stated anywhere in the Bible. As such, it should be dismissed as a post-Biblical addition to the Christian message.
Here's a book on the topic by David Bernard, a Oneness Pentecostal minister who has written dozens of books on church history: