During the Camp David Accord in 1978, President Jimmy Carter stated that President Menachen Begin, President Anwar Sadat and he got along so well together because they worship the same God. It was a truthful statement, but from a Christian viewpoint it did not contain the whole truth, and because of that, it leaned into a dangerous direction. It is true that one can state that the Jews, Moslems and Christians believe in One God. "Hear O Israel, the Lord our God is One" (Deut. 6:4). However, the Christians do not stop there. They believe that God is One, but quickly add that He is One God in three Persons - Father, Son and Holy Spirit.
A couple of months ago, I started reading an exhaustive treatise on whether one can be a Christian without believing in the Holy Trinity. The author, in a gentle fashion, was trying to prove that the Scriptures do not require us to believe in the Holy Trinity. There are subtle arguments, lengthy interpretations of the difficult passages, quotations from prestigious historians and theologians - all done to slowly move one from the Trinitarian position.
As I was reading this book, I was reminded that many years ago I read William Barclay's argument that the Church did not require us to believe in the virgin birth. The argument was disingenuous, due to the fact that one rarely can find a creed written in the first millennium in which the virgin birth is not mentioned. If the church constantly mentions the virgin birth, then one in the 20th century has to see that the church proclaimed it because it was a part of the doctrine of faith.
Sometimes people argue that one should not believe in the Trinity because it is an unexplainable doctrine. We have not been able to explain it all. However, one has to understand that monotheism, the belief in one God, was not easy to explain either. The majority of the world believed in many gods. When God commanded Moses to go and explain to Pharaoh that the God that he serves is called "I am that I am", I do not think that Moses said: Thank you God, I got it! God tells us that he is God there is no one like Him.
There were two movements in the history of Christianity to move away from believing in the Holy Trinity - one was called Arianism, who did not believe in the eternity of the Son, and the other was called Unitarianism, who became convinced that Jesus was not the Son of God, and therefore, not God. Looking at the second movement it is important to see that as soon as congregations go in the Unitarian direction, they quickly disintegrate.
Sometimes people argue that in the New Testament we have only two direct passages where the Holy Trinity is mentioned (Mt. 28:19, 2 Cor. 13:14; also Eph. 4:4-6, 1 Pet. 1:2, Jude 1:20-21). That is true, but no theologian would argue that a doctrine needs 100 verses in order to be true.We believe in the Holy Trinity because that is the teaching of Jesus Christ. Jesus Christ teaches us to honor and worship the Father, the Son and the Holy Spirit.
I think there is a great difference between not being able to comprehend the Holy Trinity and believing that it could exist because it is in the Bible, and denying the Holy Trinity because while it is in the Bible the person cannot comprehend it, and therefore it cannot exist.