Trinity
“The Christian doctrine of the Trinity holds that God is one God, but three coeternal and consubstantial persons, each corresponding to its own hypostasis: the Father, the Son, and the Holy Spirit, as one God in three Divine Persons. The three persons are distinct, yet are one “substance, essence or nature” Wikipedia

“I believe in one God, the Father almighty, maker of heaven and earth, of all things visible and invisible. I believe in one Lord Jesus Christ, the Only Begotten Son of God, born of the Father before all ages. God from God, Light from Light, true God from true God, begotten, not made, consubstantial with the Father; through him all things were made …” Nicene Creed – AD 325
“… And the Catholick Faith is this: That we worship one God in Trinity, and Trinity in Unity; Neither confounding the Persons: nor dividing the Substance. For there is one Person of the Father, another of the Son: and another of the Holy Ghost. But the Godhead of the Father, of the Son, and of the Holy Ghost, is all one: the Glory equal, the Majesty co-eternal. Such as the Father is, such is the Son: and such is the Holy Ghost. The Father uncreate, the Son uncreate: and the Holy Ghost uncreate. The Father incomprehensible, the Son incomprehensible: and the Holy Ghost incomprehensible. The Father eternal, the Son eternal: and the Holy Ghost eternal. And yet they are not three eternals: but one eternal. As also there are not three incomprehensibles, nor three uncreated: but one uncreated, and one incomprehensible …” Athanasian Creed – AD 500
The Christian doctrine of the Trinity has proved to be controversial ever since the Christian religion began 2000 years ago and in order to combat heretical teaching the two (of the three) main creeds adopted by Catholic, Orthodox, Anglican and major Protestant denominations, quoted above, were given. There have been huge disputes concerning the person hood of Father, Son and Holy Spirit, down the ages, which continue, and this has often given rise to huge disruption and schism. As far as mainstream Christianity goes, belief in the doctrine of the Trinity is an essential tenet of faith, even more so perhaps than that of Justification by Faith. Yet the word “Trinity” does not appear in the Bible and arguably it is not something that is formulated so strongly as it is in the two creeds quoted above. But as far as this writer is concerned, the doctrine of the Trinity is essential and is a key to understanding the prophets.
As far as this book is concerned, the main focus has been on God the Father, followed by God the Son and then God the Holy Spirit (dealt with in an earlier section because, even if it is only implied, the Holy Spirit played an important part in our story of the Prophets of the Bible). As far as Judaism is concerned there is only one God: “Hear, O Israel: The Lord our God is one Lord” Deuteronomy 6:4 and this message is continually reinforced by the prophets even though without exception the nations surrounding Israel worshiped other gods, sometimes many and often Israel turned to such gods. While the Christian doctrine of the Trinity is an anathema as far as much of Judaism is concerned, Christians are also monotheistic.
The expectation of the coming Messiah, which Christians see as having been fulfilled in David’s son David, who is also coming again to reign as king, was as we have discussed a major preoccupation of the prophets, harking back to God’s promise to Abraham: “in thy seed shall all the nations of the earth be blessed” Genesis 22:18, but whose expected coming intensified during and following the Exile. The Messiah was seen both in human terms e.g. “He is despised and rejected of men; a man of sorrows, and acquainted with grief: and we hid as it were our faces from him; he was despised, and we esteemed him not. Surely he hath borne our griefs, and carried our sorrows: yet we did esteem him stricken, smitten of God, and afflicted” Isaiah 53:3-4 as well as bordering on the divine: “I saw in the night visions, and, behold, one like the Son of man came with the clouds of heaven, and came to the Ancient of days, and they brought him near before him. And there was given him dominion, and glory, and a kingdom, that all people, nations, and languages, should serve him: his dominion is an everlasting dominion, which shall not pass away, and his kingdom that which shall not be destroyed” Daniel 7:13,14, but it is unlikely the prophets saw their Messiah as divine, given their belief was in the one God.
The point here is not to make a case for the Trinity in the way Christian apologists have done so in the past. While some have pointed to verses in the Old Testament that might suggest the Trinity, e.g. as part of the creation story when we read “And God said, Let us make man in our image, after our likeness: and let them have dominion over the fish of the sea, and over the fowl of the air, and over the cattle, and over all the earth, and over every creeping thing that creepeth upon the earth. So God created man in his own image, in the image of God created he him; male and female created he them” Genesis 1:26,27, when the word for God used, Elohim, suggests plurality, it would be rather stretching the point to affirm the Hebrew prophets embraced the trinitarian view.
We need to consider the New Testament to find stronger evidence to support the Trinitarian position, and several verses can be cited. Perhaps one of the strongest, and is often used, is in the prologue to John’s gospel: “In the beginning was the Word, and the Word was with God, and the Word was God. The same was in the beginning with God. All things were made by him; and without him was not any thing made that was made … And the Word was made flesh, and dwelt among us, (and we beheld his glory, the glory as of the only begotten of the Father,) full of grace and truth” John 1:1-3,14. It is often said that the synoptic gospels (Matthew, Mark, Luke) focus on Jesus humanity, whereas John’s gospel focuses on Jesus divinity and gives several examples, with the blending of the two natures being one of the great wonders. That wonderful unity can be seen in the giving of the Holy Spirit: “But when the Comforter is come, whom I will send unto you from the Father, even the Spirit of truth, which proceedeth from the Father, he shall testify of me” John 15:26. It is notable in the closing commission given to His disciples, Jesus said: “Go ye therefore, and teach all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Ghost: Teaching them to observe all things whatsoever I have commanded you: and, lo, I am with you always, even unto the end of the world” Matthew 28:19,20.
I recognise the doctrine of the Trinity is a hard one to swallow because of the impossibility of such in human terms and is one, especially those who are new to faith, may find difficult to come to grips with. But if we are to give Son and Holy Spirit the honour due to them and hold a balanced understanding of the unique parts played by Father, Son and Holy Spirit in the workings out of the universe, not least in the salvation of humankind, how each has a specific role yet ones that are beautifully complementary, an acceptance of this triune God is essential.