And it is narrated from Mujahid, concerning the interpretation of “their constitutions,” that he said: “The sphincters”—that is, the sites of the two outlets for urine and feces; when waste comes out, they constrict.

“And if We willed, We could replace them completely with others like them.” That is, if We willed, We would destroy them and bring others like them, making them their replacement.

“Indeed, this is a reminder. So whoever wills may take a path to his Lord. (29) But you do not will unless Allah wills. Indeed, Allah is ever Knowing, Wise. (30) He admits whom He wills into His mercy; but for the wrongdoers He has prepared a painful punishment. (31)”

“This” means this surah; “is a reminder”—that is, a reminder and an exhortation. “So whoever wills may take a path to his Lord”: that is, a means of drawing near through obedience.

“But you do not will”: Ibn Kathir, Ibn Amir, and Abu Amr recited it as “they do not will,” with the third-person form, while the others recited it in the second-person form. “Unless Allah wills”: that is, you do not will except by Allah’s will, for the matter belongs to Him. “Indeed, Allah is ever Knowing, Wise.” “He admits whom He wills into His mercy; but for the wrongdoers”—that is, the polytheists—“He has prepared a painful punishment.”