The rationality of religious belief systems indicates longitudinal relationships, so that each benefit from pertained rationality based on ontological place within the web of religious knowledge. Therefore, it can be possible to consider three layers of religious beliefs i.e. fundamental, middle, and marginal. Here fundamental beliefs are the most rational, followed by middle and finally marginal. Concerning Islamic and Christian traditions, there can be two beliefs, believing in one God and the hereafter, that are considered fundamental ones. There are also middle beliefs between the two mainstream religions that are about divine attributes, the relationship between God and human beings, and so on so forth. Finally, the level of marginal beliefs of two are about the sacredness of places, times, events, things, persons, situations etc. This research wants to show that although all religious beliefs have been expanded and changed under the influence of epistemic and non-epistemic factors, t fundamental beliefs have been more stable, immutable, universal, and compatible. Middle beliefs of Islam and Christianity, are generally based on believers’ plural understandings of religious texts and under aforementioned factors. Thus, in order to study the rationality of religions and their traditions, it is necessary to pay closer attention to how and under what conditions (epistemic and non-epistemic) their web of beliefs are formed and shaped.
