There's a famous yesod from Rav Chaim Brisker that the difference between the 13 Ikrim and the rest of the Torah is: that if someone doesn't know anything else in the Torah they're an Am Ha'aretz, but if someone doesn't know one of the 13 Ikrim he's an Apikorus. (And he explains thru this the Machlokes the Rambam and the Sefer Ha'Ikrim if there's 13 or 3 ikrim).