To say that you are ‘spiritual, but not religious’ could simply mean: “I am good and not bad. Please approve of me”. But it could also mean something deeper e.g. “I am willing to undermine/let go of the beliefs I already have, as an alternative to continually reinforcing old beliefs and adopting new ones” or “I am willing to try ‘wanting what I get’ (accepting) as an alternative to ‘getting what I want’ (striving)”.