Why and how did the Trinitarian monotheism develop in Christianity?

The trinitarian understanding of God did take some time to develop. This is not because it was an invention of man, it is because it’s complex. Inventions by men are easy to understand. When man makes up a god he makes it look like an animal, or a man with superhuman-like powers or immortality. Or in ignorance he shrugs it off and calls it “the absolute”. This is because when man wants to worship God but doesn’t know anything about Him, he makes god similar to himself, or something that he can easily understand.

Christianity takes what God tells us about Himself, and what He reveals about Himself in HIS WORD. Then, regardless of however difficult it is to understand, sincere believers did their best to refute false claims about Jesus and explain the amazing reality of who Jesus was and what actually happened. The trinitarian understanding of God was used very early on. In addition to all of the Bible that supports it, it was also taught by early church leaders including Clement, third bishop of Rome, AD 96; Justin Martyr, Christian writer, AD 155, Theophilus, sixth bishop of Antioch, AD 168 and others.

Christianity has ALWAYS been a monotheistic religion because of it’s foundation in Judaism. Before the trinitarian understanding of the Godhead was later understood and developed Jesus and the Holy Spirit were just mentioned and included during evangelism without getting any deeper than “the Son of God who became flesh” and “the Holy Spirit of God”. The latter was already somewhat developed because of the way The Spirit came upon the prophets to give them God’s Words. Also in the way that the Spirit of God (resided) in the Holy of Holies room in the tabernacle, while at the same time God was still supremely sovereign and in Heaven. Additionally, the promised Messiah who was to come, Immanuel I.e. “God with us” was to bring in an ETERNAL kingdom.

Jesus is A god?

From the beginning, Jesus was known to be born from the Holy Spirit of God and the Virgin Mary. Later false teachings did develop, but unlike many of today’s teachings they didn’t suggest that Jesus was just a man. After all, He was born of a virgin, did miracles, rose from the dead, etc. Many teachings were that He was a god. However, this conflicted with Judaism’s firm understanding of monotheism (as well as Jesus’s teachings Himself that there was only one God). To address the teachings of a priest named Arius, who taught that if God begat Jesus then He had an origin and was therefore a lesser god, the church held a council in Nicaea 325. At the council an overwhelming vote of 300–3 determined that Arius’s views were incompatible with what scripture shows and with what the churches were in fact teaching. The Nicene Creed was then established by the church as a formal creed officially documenting the doctrine of the Holy Trinity.

So how did it happen?

1. We know that there is ONLY ONE GOD.

   God told us there was only ONE God, and He is One. There is no god besides Him. There were no gods created before Him and there will be no gods after Him, in all of existence, in all places, in all time. He has always been God and was never anything else. God has no body, He is Spirit. (Deuteronomy 6:4, 32:39, John 4:24, 5:44, Isaiah 45:21–22, Mark 12:29, Psalm 90:2)

2. We know that the Father, Son, and Holy Spirit ARE ALL GOD.

   1. The Father is God. “Grace and peace to you from God our Father and the Lord Jesus Christ.” (1 Corinthians 1:3, See also: 8:6, Ephesians 4:4–6, Romans 15:6)
   2. The Son is God. “In the beginning was the Word, and the Word was with God, and the Word was God… The Word became flesh and made his dwelling among us.” (John 1:1–14, See also: 10:30–33, Hebrews 1:6–8, Philippians 2:9–11, Isaiah 7:14, 9:6, Romans 9:5)
   3. The Holy Spirit is God. “And do not grieve the Holy Spirit of God, with whom you were sealed for the day of redemption.” (Ephesians 4:30, See also: Acts 5:3–4, Luke 1:35, 1 Corinthians 3:16, Isaiah 40:13, Zechariah 4:6)

3. We are to worship God in Spirit and Truth.

   Jesus commanded us to baptize in the NAME OF—not name(s) of— the Father, Son, and Holy Spirit. Christian baptism identifies a person as one who believes in the Father, in the Son whom the Father sent to die for our sins, and in the Holy Spirit whom the Father and Son sent to dwell in our hearts. (Matthew 28:19)

It’s Personal.

There is only one God, yet there are 3 “distinct persons” in the one God. They are not different “beings”, they are the One being, with 3 distinct personhoods. They are called persons because they relate to each other in personal ways. The Father sent the Son (1 John 4:14). The Father sends the Spirit. (John 14:26) The Father and Son count as two witnesses (John 8:16–18). The Father and the Son glorify each other (John 17:1–5). The Spirit glorifies the Son (John 16:14). The Son speaks, not on His own, but on behalf of the Father (John 8:28). The Spirit can speak, and also does so not on His own, but on behalf of the Son (John 16:13–15). The Son asks the Father to send the Holy Spirit, so He can be our advocate (John 14:16).

The Holy Trinity.

It’s not three gods, there’s only one God. It’s not one God who took on 3 different modes or titles—they all coexist simultaneously. Jesus can’t pray to the Father if He is the Father. The Son can’t have the Holy Spirit descend on Him like a dove, at the same time the Father is speaking, if they’re in fact all the same person. It’s not 3 persons in 1 person, or 3 persons in 3 gods. It’s ONE GOD in 3 PERSONS.

However difficult to comprehend this is, it’s what Jesus taught. This is what the scriptures show us. There are multitudes of scriptures interweaved throughout every book of the Bible that support the Holy Trinity. In fact, the very difficulty of accepting IN FAITH somehow God Himself becoming flesh in order to save us from our sins is foundational to Christianity. The notion that God sent a lesser being to give him all the glory is unheard of. God gets ALL the glory! The Holy Spirit even warns us of “counterfeit Jesus’s and gospels” that would come later to deceive us with alternative understandings about God and Jesus.

“This is how you can recognize the Spirit of God: Every spirit that acknowledges that Jesus Christ has come in the flesh is from God” (1 John 4:2)

“I say this because many deceivers, who do not acknowledge Jesus Christ as coming in the flesh, have gone out into the world. Any such person is the deceiver and the antichrist.” (2 John 1:7)