1)
Why will they smash the infants against the rock?
1.
Radak: Like they were cruel to Yisrael, so will be done to them - "Hineni Me'ir Aleihem Es Madai; u'Keshasos Teratashnah u'Fri Veten Lo Yerachemu" (Yeshayah 13:18).
2.
Malbim: This is to fulfill "v'Hichrati l'Vavel Shem u'Sh'ar" (Yeshayah 14:22). Koresh returned in the second year, and totally destroyed and killed the entire nation.
