The idea of trinity was not found in the original manuscripts of the New Testament. The pronouns that refer to the holy spirit were neuter meaning "it" not "He." By the fourth century copies of the Greek started showing some of the pronouns changes from 'it" to the masculine, He. (such as Ephesians 1:14). Even in the Gospel of John the Paraclete (Advocate) is referred to by neuter pronouns and is itself a neuter noun.

The idea of holy spirit in the New Testament is demonstrated by Paul's statement in I Corinthians 2: 10 these are the things God has revealed to us by his Spirit. The Spirit searches all things, even the deep things of God. 11 For who knows a person’s thoughts except their own spirit within them? In the same way no one knows the thoughts of God except the Spirit of God. 12 What we have received is not the spirit of the world, but the Spirit who is from God, so that we may understand what God has freely given us.

The understanding of the Spirit of God is that God has a spirit like any human has a spirit. This is why we see the term is neuter throughout the New Testament. This changed when Jesus began to be viewed as divine:

John 1:18, Θεν οὐδες ἑώρακεν πώποτε ὁ μονογεν θεός, ὁ ὤν εἱς τὸν κὀλπον τοῦ πατρός, ἐκεῖνος ἐξηγήσατο.

No one has seen God at any time; the only begotten god which is in the bosom of the Father has declared Him.

With Jesus as Logos and therefore the only begotten god monotheism was compromised. For two centuries the churches wrestled with the problem. Arianism which stated about Jesus, "There was a time when he was not" and several Trinitarian theories of co-eternal existence were competing . A plethora of Trinitarian formulas were running a muck. One won politically in part because Constantine bullied the counsel to come to a conclusion so that there would be one type of Christianity. One type won. Everybody else ran or was killed as heretics over the next several years.