the key is probably that you are not reading 500 first hand accounts but instead a number that paul wrote down decades later in another part of the world not having been there himself. this also requires the literal use of "500" and "seen" which is probably a bold step when considering the motivations of the author.
i don't believe in anything religiously and am somewhat sad that i can never share the kind of faith-based community that comes about from it, but also feel that it would be dishonest to deceive myself to allow for participation in such things. i sort of feel bad about discussing my own contrary views as i have seen the value it holds for others, and do not want to dissuade them.
existentially i suppose i believe in a deterministic universe which i take to sort of imply a first motion/pre-universe state, but this is beyond description and comprehension (and inaccessible, thus lacking any purpose in worship/religion). when combined with a social constructionist approach, any sort of religious feeling of mine would probably align to upanishadic/advaita vedanta concepts of reality (tat tvam asi), but i do not see the point in artifice beyond recognition of the state at present, so i can not get behind any related modern practices.
as for why i believe this, i suppose i was raised in a manner that supported both empiricist science and periodic numinous feeling, but these are contradictory. the latter only remains in the sense that i still conceive of forces beyond the calculably apparent (but not in a way that requires divinity, instead merely that which is beyond my capacity).