How, if possible, can you determine the moral or spiritual validity of any belief system?

Belief system should be interpreted as broadly as possible in this sense. In religions, and many spiritual movements that can’t be qualified as religions per se, the basic moral lessons are based on rules and rituals, parables, etc., contained in sacred texts. Philosophers had debates that were recorded and are now distributed. Throughout time, however, these texts are subject to various interpretations – as anything written or stated invariably suffers from the fact that language confuses as much as it communicates. More recently, theorists rely not on a single text, but rather ongoing academic releases and with the advent of the internet, electronic publications of various sorts.

Considering the multitude of potential sources available, or multiple interpretations, or multiple translations…how does one determine the moral or spiritual validity of a movement or a belief. In any case, is it necessary? And if underlying texts are demonstrably flawed, does it invalidate a system, or undermine it, or demand an alternative interpretation?