Tafsir of Al-A'raf 7:117

"And We inspired Musa" — by means of an angel, as is apparent — "that throw your staff." This is the staff whose nature you have come to know. The "that" (an) is explanatory, because it follows something containing the meaning of speech without its letters. It is also permissible that it is infinitive (masdariyah), in which case the infinitive is the object of the inspiration.

The "fa" (so) in His saying—exalted is He—"So it devoured what they falsely fabricated" is fasiha (eloquent/elliptical). That is to say: He threw it, and it became a serpent, and so it immediately began devouring what they fabricated. It was omitted to signal the haste of Musa—peace be upon him—in throwing it, and the extreme speed of the transformation, as if its devouring of what they fabricated occurred immediately upon the command to throw. The present tense (yalaqafu) is used to bring the strange scene to mind.

Laqf is similar to laqfan, meaning to grasp something quickly. Al-Hasan interpreted it here as swallowing and gulping down. Ifk means to divert a thing and turn it away from its customary aspect; it is applied to lying, and it is with this that Ibn Abbas and Mujahid interpreted it, because it is turned away from its proper path. This became so famous in this usage that it became its literal meaning.

"What" (ma) is either a relative pronoun or functions as a descriptor, with the referent omitted—that is: "what they fabricate and falsify." Or, it may be an infinitive (masdariyah), which with the verb serves the meaning of the object—that is: "the fabricated," for that is what was being devoured. The majority of reciters read it as talaqqafu with a shadda, following the omission of one of the two ta’s.