Tafsir of Al-Hashr 59:21

(Had We sent down this Quran) of majestic stature, containing various forms of stern warnings, (upon a mountain) from among the mountains, or a great mountain, (you would have seen it)—despite it being a landmark of hardness and lack of susceptibility to what strikes it—(humbled, cleft asunder from the fear of Allah), that is, split apart by it.

Abu Talha read it as musadda'an by assimilating the ta into the sad. This is an allegory and an imaginative representation of the sublime status of the Quran and the powerful influence of the exhortations and deterrents contained within it. The purpose is to rebuke man for the hardness of his heart and his lack of humility when reciting the Quran and contemplating the stern warnings within it; for it is that which, had it been sent down upon a mountain, and had intellect been instilled within it, would have humbled and split asunder.

Indicating that this is an allegory is the saying of the Exalted: "And these parables We present to the people, that perhaps they will reflect." (59:21). The reference therein is to His saying: "Had We sent down..." and its likes. Thus, the speech is based on the supposition of that occurrence, or the intended meaning is "these and their counterparts." Parables are, for the most part, imaginative representations. "He is Allah, other than whom there is no deity, the One, Exalted is He, (the Knower of the unseen..."