ad,
You seem to be somewhat confused and assuming that rationalism can only be applied in one way, that is, by questioning the very basis of faith rather than a method by which one may also decipher the faith.
Nope.
First, axiomatically rationalism can only be applied in one way – rationally! Either the argument is rationally sound or it isn’t.
Second, you have this odd notion that rationalism concerns itself with faith. It doesn’t. When someone of faith thinks he has a rational argument to validate or demonstrate his faith (ie, he wants to play in rationalism's turf which, as NS tells us, is an odd notion to start with given that rationalism is itself a naturalistic concept, but anyways…) then the tools of rationalism can be brought to bear. So far as I’m aware all such arguments so far have failed, but you never know.
Third, I don’t know what your choice of faith happens to be (though I know it’s not RC) but I was struck by a catholic cleric I saw interviewed before a papal visit a while back in which he positively abjured rationalism – he rejected it as too limited in scope given his apparently superior epistemology of “faith”.
Fourth, how would you propose to use rationalism to “decipher the faith” given that it’s, you know,
faith? If that was amenable to rational enquiry, wouldn’t it be logic or science or something?
Both are acts of rationalism, even if one takes faith as granted and the other doesn't.
No, neither are. Trying to apply rationalism to matters of faith is like trying to design a building using Morris dancing. They have nothing to say to each other.
With regards to the Reformers their rationalism was that if something is not directly found in the scriptures then it is not necessary for salvation. That is a rationalism.
No it isn’t because it ignores the problems with the underlying premise. As leprechauns are by common repute musical, is it rational to think they’d take well to piano lessons?