The idea is that "marriage" should be strictly a religious matter and not recognized by the state at all — you would fill out the paperwork for a civil union and check the box "conditional upon completion of religious marriage ceremony" before you go to the church if you want what "marriage" means today. The state does not care whether your church allows inter-faith marriages or if your church even has marriage at all &mdash it is the same civil union in any case.
Apologies for furthering the off-topic diversion, but I did need to clarify that.