وَمَا خَلَقْنَا السَّمَاءَ وَالْأَرْضَ وَمَا بَيْنَهُمَا لَاعِبِينَ (And We did not create the heavens and the earth ... 21:16.) It means that we have not created the sky and the earth, and everything that lies in between them for mere amusement. In the preceding verses a reference has been made to the annihilation of certain settlements. In this verse there is a suggestion that just as the creation of the earth and the sky and all other created things was according to a set design, the destruction of the settlements was also the result of a definite purpose. Having witnessed the marvels and wonders of creation which are so abundantly spread all over, manifesting Allah's omnipotence and omniscience, do they still think that all these things are futile and without significance?
The word لَاعِبِينَ is taken from لِعَب (play), which means having no useful objective (Raghib) while لَھَو (pastime) means an act which has no purpose at all except to provide amusement in free time. The disbelievers who argue against the Holy Prophet ﷺ and the Holy Qur'an and reject the Oneness of Allah and deny His Power, despite its abundant manifestations, then it is apparent that they have a notion that all this creation is meant for amusement and pastime. The verse rejects this false view and says that Allah's creation is not for fun and pastime. A little reflection will show that even the minutest particle of the universe has its utility and each and everything created by Allah has a purpose which speaks by itself for His omniscience and Oneness.