Tafsir of Az-Zukhruf 43:2

(And the Book), meaning the Qur'an; it is intended to signify its entirety. It is also permissible that the genus is intended, which applies to some of it and all of it. It has been said: It may be that the genus of revealed books is meant, or that which is written in the Preserved Tablet, or the verbal noun meaning (the act of) writing and script. The Glorified One swore by it due to the great benefits contained within it, and that which is in that is not hidden. The former—upon the assumption that Ha-Mim is a name of the Qur'an—is that this is also intended by "the Book," and it is that by which the oath is sworn, either initially or as an amplification of what is in Ha-Mim, upon the assumption that it is in the genitive case by the elision of the oath-particle, on the basis that the basis of conjunction is difference in title; however, this necessitates the elision of the preposition while retaining its effect, as in: Kulaib gestured with the palms and the fingers. And it is part of this that one swears by two things with a single particle, which is not paid heed to. The point of repeating the oath is to exaggerate the confirmation of the oath-sentence.

(The Clear) (Meaning: Clear) to those upon whom it was revealed, because it is in their language and according to the methods of their speech, upon the assumption that it is from abāna (to be clear) in its intransitive sense. Or, (it means) that which clarifies the path of guidance from the path of misguidance, and that which sets forth the foundations of what is needed in the chapters of religion, upon the assumption that it is from abāna (to clarify) in its transitive sense.