Abstract nouns are singular in form, which means they require a singular verb. Simple as that.
The faith of Chicago Cubs fans are admirable, if not a little a bit misguided.
OR
The faith of Chicago Cubs fans is admirable, if not a little a bit misguided.
The first sentence is incorrect because faith is a singular noun, but are is a plural verb. The second sentence is correct because it matches a singular noun (faith) with a singular verb (is). The end.