John is the gospel that differs from the other three with respect to the amount of interest it has in the nature of jesus and his relationship with god. John was also the last gospel written (around 100 ce). That means that John may have been written up to 30 years after the others.
The differences in style and the late date should arouse suspicions. John is the most quoted book in relation to the trinity and the father/son nature of jesus. It may reflect a bias toward a teaching or movement that started after the first 3 gospels were written.
This is a known, debated historical fact. It isnt just me saying it. If you are heavily relying on one book, John, above all others to 'prove' a trinity, then, are you being honest with yourself? It definitely raises questions if John has such a point of difference to the other 3 books. Why dont the other 3 gospels address this extremely important topic like John does? Something fishy going on here.
John reads like it is making statements of faith and taking liberties rather than documenting events like the first 3 gospels.