Tafsir of Al-Insan 76:28

"We created them," and no one else did. "And We strengthened their structure (asrahum)," meaning: We firmly bound their joints with nerves and veins. Al-asr (the root of asrahum) originally denotes tightening and binding; it is applied to that with which something is bound and tied, as is the case here. The intention behind mentioning nerves and veins is their resemblance to the ropes with which things are tied, and the aspect of the analogy is manifest. From this, the gnostic says: "Whoever finds his bonds (asruhu) within his own essence, and his prison to be his worldly life, let him complain of the length of his days and lament his existence and his bonds."

The intention is the firmness of creation and its being well-knit and secured. From this, one says "a horse is masur al-khalq (tightly/well-knit in creation)" if it is well-secured. According to Mujahid, al-asr refers to the sphincter, and it is interpreted as the passage for waste; strengthening this means making it such that when waste is expelled, it contracts. It is not hidden that this is included within the firmness of creation and being well-knit.

"And when We will, We can replace them with others like them," meaning: We shall destroy them and replace them with others similar to them in the firmness of creation, a replacement that is wondrous and beyond doubt; this refers to the Resurrection and the second creation. Thus, the replacement is in the attributes, for the return is the same as the beginning. Because the matter is certain and inevitable, "when" (idha) is used, and the will is mentioned to leave its time ambiguous. This is common usage, just as a great person might say to someone asking for a favor: "When I will, I shall be good to you."

It is also possible that the meaning is: "And when We will, We shall destroy them and replace them with others who obey," so the replacement is in the entities. The use of "when" (idha) indicates the certainty of His, the Exalted, power over it, and the certainty of what their disbelief necessitates regarding their eradication. Thus, that which is destined and threatened is made to seem as if it were already realized, and it is expressed in terms that indicate that realization. Perhaps this is what al-Zamakhshari intended by what was reported from him: "It is only permissible because it is a threat brought forth by way of hyperbole, as if it has a specific appointed time." One should not object to this with the verse: "And if you turn away, He will replace you with another people," because subtle points (nukat) do not require universal consistency. Understand this. The first interpretation is more consistent with the context of the majestic arrangement.