The idea of this motto is that as the way people worship changes, what they believe changes too. It seems like it also suggests that as people’s beliefs change, how they worship changes. Clearly how we worship and what we believe are connected, but how tightly connected?
People can worship in a beautiful and traditional Christian church, using a beautiful traditional Christian liturgy, and yet
be crazy as snakes be no more Christian than Reformed Jews. Christians can worship in different ways and still be orthodox Christians. Bad men can put on a good show. Good men can be bad musicians.
So tentatively I think that lex orandi, lex credendi is true in the same sense that practice precedes theory. And maybe it’s just my disposition, but it seems to work more quickly in a negative way: bad practices easily disrupt worship; good practice fosters and sustains worship, but is not enough by itself.