Tafsir of Al-Mu'minoon 23:115

(Did you then think that We had created you in vain) Meaning: Did you not know something, and thus did you think that We created you without wisdom, to the extent that you denied the Resurrection?

"In vain" (‘abathan) is a circumstantial qualifier (hal) related to the pronoun of majesty (in "We created you"), meaning: "while We were playing." Or, it is a motive for the action (maf‘ul lahu), meaning: Did you think that We created you for vanity? This refers to that which is devoid of any benefit whatsoever, or devoid of significant benefit, or devoid of that which justifies the action, as the legal theorists (usuliyyun) have mentioned. Al-Khafaji favored the first meaning here, while some verifiers chose the second.

(And that you would not be returned to Us?) This is a conjunction linked to "that We created you," meaning: Did you think that [this], and did you think that you would not be resurrected?

It is also permissible that it is a conjunction linked to "in vain," and the meaning is: Did you think that We created you for vanity and to leave you without being returned? Or: "while you were playing," and [while you were] assuming that you would not be returned to Us.

In the verse, there is a rebuke for their heedlessness, and an indication that wisdom necessitates their accountability and their resurrection for recompense. The "brothers" (Hamzah and al-Kisa'i) read turja‘un (you will be returned) with a fatha on the ta’, derived from al-ruju’ (the act of returning).