Tafsir of Al-Mu'minoon 23:13

ثم جعلناه نطفة

Thereafter We made him a Nutfah. Here the pronoun refers back to humankind, as in another Ayah:

الذى أحسن كل شء خلقه وبدأ خلق اﻻنسن من طين

ثم جعل نسله من سﻼلة من ماء مهين

and He began the creation of man from clay. Then He made his offspring from semen of despised water. (32:7-8) meaning, weak, as He says:

ألم نخلقكم من ماء مهين

فجعلنه فى قرار مكين

Did We not create you from a despised water, Then We placed it in a place of safety. (77:20-21) meaning the womb, which is prepared and readily equipped for that,

في قرار مكين

in a safe lodging

إلى قدر معلوم

فقدرنا فنعم القدرون

For a known period. So We did measure; and We are the Best to measure. (77:22-23) meaning, for a known period of time, until it is established and moves from one stage to the next. Allah says here,