Properly understood, then, the desire to act justly derives in part from the desire to express most fully what we are or can be, namely free and equal rational beings with the liberty to choose.
John RawlsAny comprehensive doctrine, religious or secular, can be introduced into any political argument at any time, but I argue that people who do this should also present what they believe are public reasons for their argument. So their opinion is no longer just that of one particular party, but an opinion that all members of a society might reasonably agree to, not necessarily that they would agree to. What's important is that people give the kinds of reasons that can be understood and appraised apart from their particular comprehensive doctrines.
John Rawls