What Makes a Core Text Religious?

What distinguishes religious core texts from non-religious core texts? This question seeks a general criterion for placing core texts into the "religious" and "secular" categories. Such a criterion would guide the process of categorization with respect to particular works generally recognized as core texts. A candidate criterion might define religious core texts as core texts that contribute affirmatively to a religious view of the world. Then there would need to be a conversation about what would count as a religious view of the world and what it would mean for a core text to contribute affirmatively to such a view.