Why shouldn't I believe the Gnostic and lost books of the bible that wernt canonized into scriptures were the real testament of Jesus and Christianity instead of the others?
You'd first have to define what gnostic means.
Not every non-canonical writing falls under the category of gnostic.
The gnostic gospels, the ones which put forth gnostic ideas and theology, are not compatible with what is found in the New Testament. They can't both be true at the same time. Either the NT is true or the gnostic gospels are true.
With that in mind, you must consider that:
1. There's no evidence that the gnostic gospels were around prior to the mid and late 2nd century. In contrast, we know the authentic gospels were written in the 1st century based on early church references to them at the turn of the century as well as early physical manuscript fragments from around that time.
2. Every ancient canon list, compilation of scripture, or reference in early church writings we have all witness to the canon we have. Even when they are separated by geography and time. And this is all from the centuries prior to the Council of Nicea.
So this tells us that the early church had already known what was authentic centuries before Christianity had the power of the state behind it to enforce orthodoxy.
The men who canonized the bible chose to leave them out to stear us away from that Gospel but the Gnostics claimed they were the true Gospel as well.
Now I have to ask you if you have one shred of historical or scriptural evidence that would support your assertion that such a thing ever happened.
You won't be able to do it because all the documentation we have shows that the canon was established before the persecution of the church had stopped. The Christians of those era had no power to force certain views on anyone. That's why Gnosticism was able to rear it's head in the first place without being shut down. The only weapon the Christians had was apologetics, which is why we have writings preserved from those first couple centuries where they defend the faith against lies.
