Got a link for the statement?
It is a very provocative statement. I’ve been trying to find its original source myself, but a Googling of the quote in question provides little fruit. The best I could find for an original citation was “St. Catherine of Siena, SCS, p. 201-202, p. 222, (quoted in Apostolic Digest, by Michael Malone, Book 5: “The Book of Obedience”, Chapter 1: “There is No Salvation Without Personal Submission to the Pope”).”
But this doesn’t seem to be a primary source. At least I’m not sure what that citation means. Does it mean the quote is found on pages 200-201, 222 of “St Catherine of Siena, SCS”, (whatever that is) or in the other work? Also, the pages mentioned seem odd, as if it’s a reference to the quote, but not the entire writing.
A reading of the entire writing where the excerpt is found is clearly required. From a Googling of the quote in question, it seems clear the topic St Catherine was writing about was obedience to the Pope. Thus the context may be hyperbolic in nature, to drive home a point. Indeed, Catholic teaching itself makes it impossible for the Pope to ever be “Satan Incarnate”. So to believe St Catherine was actually suggesting this as a possibility is illogical, to say the least. Again, she must have been making a broader point using hyperbole.
A thorough reading of the quote in context is required before such a quote can be used to discredit St. Catherine of Siena’s ability to reason.