Tafsir of Al-Mu'minoon 23:115

أفحسبتم أنما خلقناكم عبثا

Did you think that We had created you in play, means, `did you think that you were created in vain, with no purpose, with nothing required of you and no wisdom on Our part!' Or it was said that "in play'' meant to play and amuse yourselves, like the animals were created, who have no reward or punishment. But you were created to worship Allah and carry out His commands.

وأنكم إلينا ﻻأ ترجعون

and that you would not be brought back to Us! means, that you would not be brought back to the Hereafter. This is like the Ayah:

أيحسب اﻻنسن أن يترك سدى

Does man think that he will be left neglected! (75:36)