1)
Why does it mention "Zarah" and "Nochriyah"?
1.
Malbim: Afterwards you will be more wayward to hug a Nochris, who is worse than a stranger - she is "Bas El Nechar" (Mal'achi 2:11).
2.
Malbim (according to Melitzah): Zarah is deceptive Chachmos. Why err in them, after you find Chachmah and Da'as in Toras Hashem?! Nochriyah is teachings of heresy and denial, that you will embrace them afterwards.