כִּי־אֵשׁ֙ קָדְחָ֣ה בְאַפִּ֔י וַתִּיקַ֖ד עַד־שְׁא֣וֹל תַּחְתִּ֑ית וַתֹּ֤אכַל אֶ֙רֶץ֙ וִֽיבֻלָ֔הּ וַתְּלַהֵ֖ט מוֹסְדֵ֥י הָרִֽים׃
Poiché un fuoco è acceso nella mia narice, e brucia nelle profondità del mondo inferiore, e divora la terra con i suoi prodotti, e getta a fuoco le basi delle montagne.
Sforno on Deuteronomy
כי אש קדחה באפי, for when I disciplined them in order to induce them to repent their sins this people lit a fire in My wrath ותיקד עד שאול תחתית, they heaped sin upon sin until My wrath burned to the very bottom of Sheol, (lowest layer of purgatory). In other words, their punishment would consist of being consigned to this lowest region of purgatory. (compare Chronicles II 28,22 describing Achaz adding sins as a result of his kingdom having been severely chastised by G’d.)
Siftei Chakhamim
Down to the foundation. He added the words “you” and “your land” for without this we would not know who would be burned or which land.