Sforno on Deuteronomy 32:22/ספורנו על דברים ל״ב:כ״ב

1כי 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.)

2ותלהט מוסדי הרים, it burned and consumed down to the foundations of the mountains. The “mountains” are a simile for the high-ranking personages, all of whom were the first ones to be exiled prior to the destruction of the first Temple. (compare prediction by Isaiah 3, 1-3)