It will besiege you in all your cities until the collapse of your high and fortified wall in which you trusted throughout your land. It will besiege you in all your cities in all your land which Hashem…has given you.
Be’er Yosef: The verb in the text is redess, and its meaning is not so clear. Rashi, citing Onkelos, takes it to mean overpowering, conquest. The enemy will lay siege until they succeed in overcoming the walls.
Based on a midrash we could suggest a different translation. Redess might mean lowering, as will be explained.
After three and a half years of surrounding Yerushalayim, Nevuzradan was on the verge of giving up and returning to Nevuchadnetzar. Before that could happen, however, he observed that the walls that he had found to be impenetrable were slowly but steadily sinking. He changed his mind, and waited long enough to have much easier access to the city, which he then entered and conquered.
Following the implications of this thought we discover new meaning in the end of our pasuk. What does the Torah convey to us by adding, “in all your land which Hashem…has given you?” We might recall, though, another time and place where walls were swallowed in their places. The gemara tells us that this was precisely the fate of the walls of Yericho. The huge walls were as thick as they were tall; had they simply toppled and fallen, their new height would have been their old width – and just as tall as they had been before falling! Rather, says the gemara, the walls were swallowed in place. The end of our pasuk might mean that what happened in the process of taking possession of “all the land which Hashem has given you,” i.e. that walls sank into the ground, would now take place with the walls of your cities, to aid your enemies.
The purpose of such miraculous treatment of the city walls seems apparent. Hashem made it clear to the conquering enemy that his own power was insufficient to take Yerushalayim. He would have failed to penetrate the walls, were it not for G-d miraculously giving him access. Indeed, the gemara reports that a voice from Heaven announced at the time of the destruction, “You have killed a dead people. You burned a burnt Heichal; you have ground flour that was already ground.”
We are only part of the way there, however. Demonstrating to the enemy that his own force could not have dislodged the Jews from their capital strikes us as appropriate. It does not explain why Hashem chose sinking walls to drive this lesson home. Many other ways could have conveyed the same message.
Shir Hashirim speaks of a wall with towers. The wall, explains the gemara, is Torah, and the towers are, following different interpretations, Torah scholars and places of davening and learning. They offer the real protection to the city. A midrash takes this to the next step. The Land was not lost because of idolatry, murder and immorality. Somehow, HKBH would have tolerated them. When the Torah is poorly treated, however, Hashem removes His protection, potentiating the designs of our enemies.
In other words, when the Torah and its adjuncts – talmidei chachamim, yeshivos, shuls – are underappreciated, the protection they offer is reduced, endangering the inhabitants. Undervaluing Torah, reducing its importance and stature, casting it to the ground, as it were, brings a Divine response that is measure for measure.
When the real protectors of society are lowered to the ground, then their surrogates – the physical walls – follow suit. They find themselves as well sinking into the earth.
 Based on Be’er Yosef, Devarim 28:52
 Pesicha to Midrash Eichah
 Berachos 54B
 Sanhedrin 96B
 Shir Hashirim 8:10
 Bava Basra 7B
 Eichah Rabbah, Pesichah