I do not discuss the attributes of God nor if there is a God or a Nirwana, or if Christians are right or Muslims.
The question is what are the sources we can use and how reliable are they.
If you say that tradition or holy books are a good source then I agree. However there are many different and they do not all say the same thing.

If there is a God (whatever that is) and is somehow in connection with us then there should be the chance to get at least some information.

I know that in Middle Age there were Christions who chose the mystic way and others who have a more intelectual approach. Even others relied on the authorities.

Even if you do not believe that there is a kind of God, how do you get this point of view?