Tafsir of Al-Muddathir 74:49

The Fa in His saying, "So what is [the matter] with them, [that they are] turning away from the reminder," is for connecting the denial of their turning away from the Quran—without any cause—to what precedes it regarding the justifications for approaching it and taking heed from it, specifically the wretched state of the deniers.

"Turning away" (mu'ridin) is a circumstantial qualifier (hal) necessitated by the pronoun in the prepositional phrase that serves as the predicate for the interrogative Ma (i.e., lahum), which is the intended focus of the discourse. "From the reminder" ('an al-tadhkirah) is connected to it, and the advancement [of the prepositional phrase] is for the sake of emphasis, while also observing the rhythmic ending of the verse (fasilah).

This means: If the state of those who deny it is as mentioned, then what has happened to them that they turn away from the Quran despite the supporting reasons for approaching it and the gathering of motives for believing in it? It is permissible that "the reminder" be intended to encompass the Quran and what is beyond it, though the first [the Quran] is more likely. It is a verbal noun (masdar) in the meaning of "reminding," applied to that which is mentioned as an intensification [of the meaning].