Science is the empirical study of how things are. Religion is the normative study of how things should be.
Except that religion can't help but make empirical claims that routinely contradict the reality science reveals to us, and quite often in extremely absurd ways. If you want to subtract all the ridiculous claims of religion and jettison the supernatural elements and say instead that religion is "the study of how things should be" then you've just described moral philosophy. I've no problem with moral philosophy as such, but I have not seen anyone actually behave as if that's all they believed religion was.
It's all well and good to quote-mine the bible and say everything else is just details, except when the overwhelming majority of your fellow believers use those details to justify very damaging and immoral behaviour. And if the foundation of your morality is divine authority and the immoral prescription is in your holy text (and the new testament is hardly the moral exemplar), you have very little cause to argue with them.