Tafsir of Al-Qasas 28:50

"But if they do not respond to you"—that is, if they do not do what you have tasked them with: bringing a book better guided than those two. The term "respond" (istijabah) is used here to signal that he—peace be upon him—was in a state of absolute certainty regarding his command; for his command to them to bring what was mentioned was an invitation to something he truly desired to see realized.

It has also been said: The meaning is, "If they do not respond to your invitation to them toward faith, after the miracles contained in the Book you brought them have been made clear to them." Thus, "responding" is taken in its literal sense, as faith is something he—peace be upon him—truly desired for them to embrace. As stated in Al-Bahr, it bears the meaning of ijabah (answering). It takes the inviter with the preposition lam (li), as in this verse and the words of the Almighty: "So his Lord responded to him," and His saying: "And We responded to him." It also takes the inviter directly, as in the line of poetry from Al-Kitab: "And a caller called, 'O you who answers the call,' yet no one answered him at that moment."

Al-Zamakhshari stated: This verb takes the du’a (the call/prayer) directly, and the caller with the preposition lam. Usually, the du’a is omitted when it is linked to the caller; thus, one says, "Allah answered his prayer" or "He answered him." It is rarely said, "He answered him his prayer." His statement in the verse—falam yastajibhu—is a case of an omitted genitive, meaning "he did not answer his prayer." If the pronoun in yastajibhu were assigned to the "call" understood from the "caller," there would be no need for the estimation of an omitted word. The object here is omitted due to the mention of the caller; the reasoning, as some have said, is that when both the caller and the act of responding are mentioned, the object must be the "call," making its explicit mention redundant. It is also permissible that the omission is due to it being known from the action itself, not because the caller was mentioned. This ruling applies to istijabah but not to ijabah, as per the Almighty’s saying: "Answer the caller of Allah."

"Know then that they only follow their own desires"—which are deviant, without having any foothold or basis whatsoever; for if they had one, they would have produced it.

"And who is more astray than he who follows his own desire"—this is an interrogative in the sense of denial, meaning: there is no one more astray than he who follows his desire without guidance from Allah. That is, he is more astray than every other astray person, even though the structural form is intended to negate the existence of someone "more astray," not to negate the existence of an equal, as has been discussed repeatedly in similar contexts.

The Almighty’s saying, "without guidance from Allah," is in the position of a state (hal) describing the subject of "follows." The qualification of following with this phrase is for the sake of added emphasis and further indictment and condemnation; otherwise, the impossibility of his following (desire) while having guidance from Allah is self-evident. It has also been said that it is to provide an exception for instances where there might be guidance from the Almighty—as a person may sometimes follow his own inclination and it happens to coincide with the Truth, though this is a point of contention.

"Indeed, Allah does not guide the wrongdoing people"—those who have wronged themselves by plunging into the following of desire and turning away from the verses that lead to the manifest Truth.