al-Qamar 54:18

Kadhdhabat ʿĀdun fa-kayfa kāna ʿadhābī wa nudhur "ʿĀd denied. How then were My punishment and My warnings!"

This verse is the most striking choice in the structure of the sūra, and I gave it in tabular form above: the punishment refrain has been placed at the beginning of the account, not at its end.

In the other three accounts the order is: name of the people → offence → punishment → refrain. Here the order is: name of the people → refrain → description of the punishment → refrain.

The result: the account of ʿĀd becomes nothing but a three-verse description with the same sentence set on either side of it.

I record this as my own reading: this arrangement puts verses nineteen and twenty inside a parenthesis. The question is asked and answered, then the question is asked again. The reader therefore reads the description as the answer to a question asked twice.

And this has to do with ʿĀd's being the shortest account. A narration of three verses may have been framed so that it should not be lost. This last sentence is a conjecture and I present it as one.

The people of ʿĀd and Iram were treated in detail in al-Fajr: where the people lived, the meaning of the expression dhāt al-ʿimād, the disagreements about them and the historical background are given there. In al-Ḥāqqa the destruction of ʿĀd was taken up in detail: the singular form of rīḥ, ṣarṣar, ʿātiya, ḥusūman, ṣarʿā, aʿjāzu nakhlin khāwiya.

I do not repeat these two. Below I give only what belongs to al-Qamar.

In the section on al-Ḥāqqa this observation was recorded and it holds here too: al-Fajr named ʿĀd by what they did, al-Ḥāqqa by what befell them. Al-Qamar does a third thing: it mentions neither what they did nor what they built. In al-Qamar ʿĀd has a single act: kadhdhabat — they denied.

Three sūras take three different faces of the same people. And the face al-Qamar takes is the one that suits this sūra's list: the sūra lists peoples by their common act.