What is it to be Christian ?

This is why the Thomas books were not included in the Nicene Creed. IMO, that it has to to with the divinity of Christ is BS. There are other references in included text to Christ as a man.
The reason was all the referenced to the individual relationship between the individual and God and how all people are to be lead to God, not just a select few or ANY form of specific inclusion.
Really, this is the core of what pissed-off the Jewish authorities. His teaching that they were not special.
The Gospel, on many levels, threatens the Church's role in faith, Paul's legacy, and the true nature of Christ in the Church's view (it must remain as unattainable as possible to keep the rubes payin'-up and the butts in the pews).