وَسُيِّرَتِ الْجِبَالُ فَكَانَتْ سَرَابًا
and the mountains will be set moving and become a mirage.
Agha Ali Puya Commentary
Commentary on Quran 78:20
[Pooya/Ali Commentary 78:20] Aqa Mahdi Puya says: Mountains give the idea of firmness and stability, but they will vanish on the day of resurrection as if they were a mirage which means everything material is transitory.