Tafsir of Ar-Rum 30:34

(To disbelieve in what We have given them) The lam (prefix letter) here is for the consequence (al-aqibah). The claim that it necessitates a period of delay—and is therefore called the "lam of outcome"—given that polytheism and disbelief are proximate to one another with no delay between them, as has been said, has no basis.

It is also said: It is for the imperative, and it serves as a threat, as one says in anger: "Disobey me as much as you can." This is appropriate for His, the Glorified, saying: "So enjoy yourselves," for it is an imperative of threat. As for the possibility of it being a past-tense verb conjoined to "they associate partners," its state is well-known [i.e., rejected].

The fa (in "So enjoy") denotes causality. Tamattu (enjoyment) means to take pleasure. There is a shift in it from the third-person to the second-person address: "Then you will come to know," the consequence of your enjoyment.

Abu al-Aliyah read it as yumatta’u (they are made to enjoy) with a ya prefixed and the verb in the passive voice, and it is conjoined to yakfuru (that they may disbelieve). Correspondingly, he read sa-ya’lamun (they will come to know) with a ya.

It is also reported from Abu al-Aliyah: fa-yatamatta’u with a ya before the ta, and it is also conjoined to yakfuru.

From Ibn Mas’ud: wa-li-yatamatta’u with the lam and the ya, and it is conjoined to li-yakfuru.