To describe a foreign belief system accurately, translate its own authoritative texts rather than relying on hearsay, and report doctrines as their adherents hold them before adding any critique. This method separates the task of understanding from the task of judging, so that disagreement does not distort the record of what is actually believed.
A people can be barred from outside knowledge not by any single cause but by a cluster: linguistic difference, religious prohibition on sharing learning with outsiders, caste restrictions, and a cultivated conviction of their own uniqueness. These factors together make a society intellectually self-enclosed, so that even its own learned members may not recognize what others possess.
The same society can hold a mathematically precise astronomy among its specialists and a mythological cosmology among its priests and poets, with the two coexisting unreconciled. Reading a culture requires distinguishing which of its voices is speaking, because the educated calculation and the popular story often contradict each other on the same subject.