Tafsir of Al-Balad 90:20

Upon them is a great fire, mu'sadah (closed in), meaning covered over. It is said: "I closed the door (asadtu al-bab)," if you shut it and covered it. This is the dialect of Quraysh, according to what has been narrated from Mujahid. The manifest implication of the words of Ibn Abbas is that it is not exclusive to them [the dialect of Quraysh]. Among such usage is the saying of the poet: "My she-camel yearns for the mountains of Makkah, while behind her are the doors of San’a closed (mu'sadah)."

It is also permissible that it is derived from awsadtu (I closed), in the sense of locking, with a hamza (glottal stop), similar to the reading of one who reads al-su'q (the shank) with a hamza. More than one of the seven reciters read mu'sadah without a hamza, so it appears it is derived from awsadtu. It is also said it may be from asadtu with the hamza softened. The poet said: "A people whose children treat lice and smooth chains and a closed (mu'sadan) door." The intended meaning is that its doors are locked. They were locked only to intensify the torment—may Allah the Exalted protect us from it—upon them.

The threat against them was stated explicitly, while the promise to the believers was not stated explicitly, because that is more appropriate to the context for which the speech was brought and is more in agreement with the purpose and objective. For this reason, the separating pronoun (damir al-fasl) was brought with them to denote restriction (hasr). They were considered as if absent, in such a state that they are in no way fit to be pointed to. This path was not taken in the first sentence regarding the believers.

It is narrated from al-Shamani that he said: "The wisdom in omitting the separating pronoun in the first two instances and bringing a demonstrative pronoun in its place is that the demonstrative pronoun is brought to distinguish that which is intended with the most complete distinction, as in his saying: 'This is Abu al-Saqr, alone in his merits / from the offspring of Shayban, between the thorn-tree and the Muslim.' The pronoun is not like this, for the distant demonstrative pronoun serves to express exaltation, by treating the loftiness of the status of the one pointed to as if he were at the peak of his rank. Thus, the demonstrative pronoun is for exaltation and for pointing to their distinction and their deserving the most complete fame, unlike the people of the left hand, and the pronoun does not provide this."

End of quote. In this, there is the rebuttal that just as the demonstrative pronoun provides exaltation, it also provides belittlement, as in the saying of Allah the Exalted: "For that is the one who drives away the orphan." Furthermore, complete fame in evil is like complete fame in good, so what is the obstacle to considering their deserving of complete fame in evil? In sum, what they mentioned is of no consequence, and perhaps what we have mentioned is the most appropriate. So contemplate it.