﴿ وَجَعَلْنَا ٱلسَّمَآءَ سَقْفًۭا مَّحْفُوظًۭا ۖ وَهُمْ عَنْ ءَايَٰتِهَا مُعْرِضُونَ ﴾

“and [that] We have set up the sky as a canopy well-secured? And yet, they stubbornly turn away from [all] the signs of this [creation],”

وَجَعَلْنَا فِي الْأَرْ‌ضِ رَ‌وَاسِيَ أَن تَمِيدَ بِهِمْ (And We created mountains on the earth, lest it should shake with them. 21:31) The word مَید (mayd) in Arabic language means to be convulsed. Therefore, the meaning of this verse is that Allah Ta` ala has planted mountains on the earth to hold it in place because any violent movement of the earth would be catastrophic to those who live on it.