al-Naḥl 16:70

Wa'llāhu khalaqakum thumma yatawaffākum, wa minkum man yuraddu ilā ardhali'l-ʿumuri li-kay lā yaʿlama baʿda ʿilmin shayʾā, inna'llāha ʿalīmun qadīr

"God created you, then He takes you. And some of you are sent back to the most abject stage of life, so that after knowing they should know nothing. God is knowing, all-powerful."

The root ر-ذ-ل was treated at al-Shuʿarāʾ, 26/111 (wa'ttabaʿaka'l-ardhalūn): what is worthless, low, of no use in a thing; ardhal — the elative: the lowest. And this verse was already named there. I rely on that treatment.

And at al-Tīn, 95/5 (thumma radadnāhu asfala sāfilīn), this verse was used in a table of disagreement as evidence for one of the readings: the sense of the verb radda as "turning back, returning" and its use in this verse were recorded there. I rely on that treatment.

What belongs here is that the sentence is built on the axis of knowledge, and this must be recorded:

Li-kay lā yaʿlama baʿda ʿilmin shayʾā — "so that after knowing he should know nothing."

Decline, then, is described not as a weakness of the body but as the taking back of knowledge.

And this has a counterpart within the sūra. The seventy-eighth verse will build the same axis from the other end: wa'llāhu akhrajakum min buṭūni ummahātikum lā taʿlamūna shayʾā.

This is an overlap verifiable within the sūra, and eight verses stand between the two. I record this as my own reading: the sūra bounds a human life at both ends with the same word (shayʾā — nothing at all). At the beginning nothing is known; at the end what was known is taken back. And what is given in between will be enumerated in the seventy-eighth verse: hearing, eyes, hearts.

At al-Rūm, 30/54, the three stages of life (weakness → strength → weakness and grey hair) were treated and compared with the six steps at Ghāfir (al-Muʾmin), 40/67. I rely on that treatment and record the difference here: al-Rūm and Ghāfir measure the stages by the body; al-Naḥl by knowledge.