Radak: When all of Yisrael were in their land, they did not want to repent. even though I warned them constantly via My Nevi'im, and I made their enemies rule over and plunder them, so they would be chastised, they did not repent. All the more so now that the became used to their evil deeds, to the point that fire consumed all around them and all of Eretz Yisrael was destroyed, except for Yerushalayim. They hardened their hearts until Isur became like Heter for them. The became used to the evil deeds of the Goyim. They said, the Goyim succeed in their deeds ? also I will do so! So Achaz said when Melech Aram fought him ? "Elohei Malchei Aram Mazerim Osam Lahem Azabe'ach v'Yazeruni" (Divrei ha'Yamim II, 28:23). Therefore, there is no hope for them. They were singed from the fire, and did not feel it. Therefore, the fire will consume them.

Rashi: This is a Kal v'Chomer - all the more so. We find this in all of Tanach, e.g. "Anachnu Fo bi'Yhudah Yere'im v'Af Ki Nelech Ke'ilah" (Shmuel I, 23:3).