In chronological order, Mark wrote the first of the Gospels. Nowhere in the Gospel of Mark does he claim that Jesus Christ is the Messiah. Later Gospels incorporated that thought into their writings. Furthermore, it is noted that in his Gospel, Mark writes nothing about Christ’s resurrection. In his mind, was Mark just writing the history of a man? He certainly does not seem to have been writing about "a God" who is equal with the Father!
The Church, as a group, did not accept that Christ was God until about 300 years after Christ’s death. At a council meeting in 325 AD, the Church leaders made it official that the church believed that Christ also was God. It was in 381 AD that the church finally, officially stated that God consisted of three persons.
Perhaps it is no wonder that the theory was accepted as quickly and as widely as it was because Athanasius, a leader in the church at that time, would try to destroy those people who did not agree with his heretical, theological trinitarian views. About Athanasius, Wikipedia writes, there were allegations of defiling an altar, selling Church grain that had been meant to feed the poor for his own personal gain, and for suppressing dissent through violence and murder. He also was accused of threatening to interfere with the supply of grains from Egypt. If this accusation is true, his reason for doing that, probably would have been to starve those Christians in Europe who did not yet agree with his theology concerning the trinity.
By the year 381 AD, the African Christian church had already imported so many doctrines from the African pagan culture that it was an insignificant thing for them to add another teaching to their already “non-Christian” set of beliefs. Therefore, accepting the doctrine of the Trinity would have seemed like a small step.
Even under the threat of persecution or death, there were some who followed Arius who insisted that God is not a trinity. He taught that Christ is the Son of God, but not God himself. Based on the teaching of the New Testament it seems obvious that Arius and his followers were on the right path and the church took a wrong turn way back in the fourth century. Sir Isaac Newton expressed that same thought in these words, Christianity went astray in the 4th century AD, when the Council of Nicaea propounded erroneous doctrines of the nature of Christ.
About Eusebius, Bishop of Caesarea, at the end of the fourth century, we find this interesting bit of history. Before the meeting of the council, he had intervened on behalf of Arius, and had remonstrated with Alexander ... for deposing him (Arius). By the more vehement enemies of Arianism he (Eusebius) was regarded with great distrust. When the creed of Caesarea had been modified ... (to include the words stating that the Son was) “of the substance of the Father,” “begotten not made” ... Eusebius hesitated whether he should subscribe it. He did not like the new terms; ... But after a day’s consideration he signed with the rest, and in a letter to the people of Caesarea he explained that, “though he would resist to the last any vital change in the traditional creed of his Church, he had nevertheless subscribed to these alterations, when assured of their innocence, to avoid appearing contentious. So the creed which changed Christ from being the “Son of God” to being equal with God, happened, in part, because one leader in the church did not have the backbone to stand up for what he believed to be right!
1 John 5:7, as it is in the KJV, is almost sure proof of the validity of the doctrine of the trinity; For there are three that bear record in heaven, the Father, the Word, and the Holy Ghost: and these three are one. But, newer, more accurate, translations have taken all the vitality for that argument out of that verse. The new translations are much condensed and they say nothing about the Father, the Word, and the Holy Ghost: and these three are one. There is nothing there about three being one. Note: The Living Bible - So we have these three witnesses.
The New Living Translation - So we have these three witnesses.
The New Revised Standard Version - There are three that testify.
The Jerusalem Bible - So that there are three witnesses.
Then, in verse 8, John tells us what the three witnesses are, and they are NOT the Father, the Son and the Spirit; They are the Spirit, the water, and the blood.
About 1 John 5:7 the Wycliffe Commentary. writes, The text of this verse should read, ‘Because there are three that bear record’. The remainder of this verse is spurious. Not a single manuscript contains the Trinitarian addition before the fourteenth century, and the verse is never quoted in the controversies over the Trinity in the first 450 years of the church era.
About verse 7 Jerome Smith writes, “...if it was admitted as the Word of God, all the ingenuity and diligence of opponents could scarcely avoid the inference (that there is a Trinity) naturally deducible from it. Contemporary scholarship, however, fails to support this reading in any form, suggesting it was added to a late Greek manuscript made for the purpose to influence Erasmus to include it in his Greek text, for Erasmus had promised he would include the text if even one Greek manuscript could be found which contained it. It seems as if such a Greek text did not exist to prove the doctrine of the Trinity, so someone put those words into a Greek manuscript. Erasmus, not willing to break his promise, had to include the following words into his translation, in heaven: the Father, the Word, and the Holy Spirit: and these three are one.
It has also been alleged that at the time Jerome was translating the Greek Bible into the Latin Douay version, the debate over the Trinity was in full swing, so Jerome thought he would bring the debate to an end, once and for all, by adding to the Bible the words, in heaven: the Father, the Word, and the Holy Spirit; and these three are one. It is interesting to note that the Douay-Rheims translation does include the words And there are three who give testimony in heaven, the Father, the Word, and the Holy Ghost. And these three are one, but in the commentary of this section they completely neglect to say anything about this verse. It seems as if they knew that those (implanted) words did not belong in the Bible.
Before Jerome’s translation verse 7 simply said, “So there are three that testify”. He added words to the Holy Scriptures just to foster his (the church’s) theology. Yet, we (Protestants) still insist that the Bible is inerrant and that these verses prove the doctrine of the trinity. The founder of the Jesuit community was dead right in stating the Roman Catholic position on doctrinal issues, when he wrote, if [the church] shall have defined anything to be black which to our eyes appears to be white, we ought in like manner to pronounce it to be black. It seems that the Protestants have taken the same view about the doctrine of the trinity. Even though the Bible does not teach the doctrine of the trinity, we are told that it is what we need to believe, and we feel like heretics if we do dare change our stance. When the reformers left the Roman Church, they should have left the doctrine of the trinity, with other erroneous doctrines that they did leave, on the Roman garbage heap!