Rav Tzadok haCohen in Peri Tzaddik on Vayishlach, section 11, last paragraph, discusses that Persian/Medean exile corresponds to Yaakov avinu.
In passing, he discusses the Talmud (Bavli Berachos 8b) which first quotes Rabban Gamliel who says that he likes 3 aspects of Persian conduct because they are modest, and right after, the Talmud quotes Rav Yosef that the Persians are designated for Gehinnom.
Rav Tzadok resolves the seeming contradiction by saying that their modesty leads them to Gehinnom because it is not migeder kedushah.
Could someone please explain what he means, and possibly explain how modesty (when not applied in a fake way to lead to more immodesty) can be not from the aspect of kedushah?
Thank you very much.