So here's a little thought experiment: Imagine that we really did have good reasons for thinking both the Bible and the early church councils to be divinely inspired. Imagine that the Bible made lots of incredibly precise and accurate predictions about the future, and that the councils knew about all sorts of science that they couldn't possible have known about at that time. So, given that the Bible and the church councils seem to have some kind of divine or higher power behind them, it may be rational to believe what they have to say about hell, the trinity and Jesus.
But of course this is not the situation we find ourselves in, and so both fundamentalist Christians and fundamentalist Muslims are irrational to believe their doctrines based on what's been passed down through scripture and tradition.
IMO most Christians would say the primary purpose of the Bible is not predicting the future or teaching science. So you ought to use different criteria in your thought experiment such as does Christianity improve society, personal happiness, and so forth. It is somewhat rational to think the Bible might be telling the truth about heaven if people who believe the Bible about more practical matters such as personal behaviour have found it to be true.
We can't really say the Christian tradition must be divinely inspired because it produces social stability and personal happiness and turns people's lives around, getting them off drugs or alcohol or whatever, The reason for this is that other religions like Islam, Mormonism and Scientology also seem to do all of these things. And we also can't say the Bible must be divinely inspired because it moves people, is so beautifully written, changes lives etc, since many other books do these things too. That's why I chose the criteria of amazing predictions and astounding knowledge for divine inspiration, and indeed this is why many fundamentalist Muslims and Christians use these criteria. They know they need to try to find something that's unique to their tradition.