they only developed AFTER all the apostles were gone.
The oldest pieces of christian writings apart from the NT is a short book called The Didache. In its 10th chapter it says:
We thank you, Holy Father, for your holy Name which you have made to dwell in our hearts; and for the knowledge and faith and immortality which you have made known to us through Jesus your Servant. Glory to you forever! You, Almighty Master, created everything for your Names sake . . . And to us you have graciously given spiritual food and drink, and life eternal through Jesus your Servant.
Jesus here is described, not as an equal part of God, but as a 'servant' of God. There is no trinity idea expressed here just as there is no trinity expressed in the NT.
Clement of Rome is one of these earliest (100ce) apostolic fathers and he also does not imply any kind of trinity in his writings. In 'First Epistle of Clement to the Corinthians' he states:
Christ therefore was sent forth by God, and the apostles by Christ....May God, who seeth all things, and who is the Ruler of all spirits and the Lord of all fleshwho chose our Lord Jesus Christ...We will beg with earnest prayer and supplication that the Creator of the universe will keep intact the precise number of his elect in the whole world, through his beloved Child Jesus Christ. . . . We realize you [God] alone are highest among the highest"
Clement certainly was not of the opinion that Christ was equal to God and he didnt even mention the holy spirit as a 'person' in any shape or form. Ignatius was another very early christian writer who failed to mention that the holy spirit was a person.
But now come forward to the 2nd century and we have the apologists...men such as Justin Martyr, Tatian, Athenagoras, Theophilus, and Clement of Alexandria and Tertullian.
In Dr. H. R. Boer, in his book A Short History of the Early Church, comments on the thrust of the Apologists teaching:
Justin [Martyr] taught that before the creation of the world God was alone and that there was no Son. . . . When God desired to create the world, . . . he begot another divine being to create the world for him. ...Justin and the other Apologists therefore taught that the Son is a creature. ...The Son is subordinate, that is, secondary to, dependent upon, and caused by the Father. The Apologists were subordinationists.
Even Tertillian who many believe was a trinitarian because he was the first to use the word trinitas was still far different to christendoms trinity. He viewed the Son as subordinate to the Father. In his writing 'Against Hermogenes' he wrote:
We should not suppose that there is any other being than God alone who is unbegotten and uncreated. . . . How can it be that anything, except the Father, should be older, and on this account indeed nobler, than the Son of God, the only-begotten and first-begotten Word? . . . That [God] which did not require a Maker to give it existence, will be much more elevated in rank than that [the Son] which had an author to bring it into being.
But now come forward again to the 3/4rd centurys with men such as Athanasius the bishop of Alexandria, Basil the Great, Gregory of Nyssa, Gregory of Nazianzus, Ambrose of Milan and Augustine of Hippo and you'll see that they formulated the idea of God, Jesus and Holy spirit all being equal and one...one god with 3 faces.
So what im trying to show is that the further back you go, the closer the writers were to the NT...but as we come forward in time, later church fathers began to change from the NT to a lot of ideas that were not based on the NT writings and its quite a well known fact....this is why a christian should not be using their teachings as a basis for their faith...the bible should be the basis for our faith, not the men who changed the theology.