Well I submit to you that it's impossible to understand 70% of the New Testament without studying the Gnostic texts. There are scriptures authored by the actual Apostles who walked with Jesus (like the Gospel of Thomas), & writings from his brother James among others.

All these Christian sects that claim these things aren't Biblical have been seduced into false doctrines. They're so brainwashed they won't even bother to look at these writings. Of course, when you say these things to them, they're insulated from reality by that very same brainwashing... "Oh no! He's of the devil! He's pushing fake scriptures & I'll burn in hell if I even dare look at it! My pastor warned me about this!" Very sad stuff.

Many of the ancient works these people have been terrorized into never looking at are the very same works that would strengthen their faith into an unbreakable link to the living God & his son, our Savior, Jesus Christ.