The bedrock “scriptures” of Hinduism, the Upanisads, are experiences; spontaneous expression of deep spiritual insight. Unlike Western philosophy they are not products of discursive intellect. Nor are they mere recording of historical events, however spiritual such events might be. Both intellectual exercise and historically accounts can be grasped and understood, leaving no mystery remaining. Whereas spiritual insight, inner illumination, remains a mystery no matter how much one talks about it. It is a place to go, now, not something to merely think about or remember. And having gone there one is mystified even as one is enlightened.
The Upanisads are a result of what they invite others to do: partake of a first person methodology for exploring the mystery of consciousness, the one mystery that remains standing despite the committed effort to demystify it. It is the last frontier. And it is both things at once–static and dynamic/orthodox and innovative. This is the very nature of reality, of life.