"And the heaven will split asunder, for that Day it will be frail" (69:16), similar to His saying: "And the heaven will be opened and will become gateways" (78:19), meaning: its splitting. "Al-wahiyah" (the frail) means the weak; it will not be in the state of firmness as it once was.
﴿وَانْشَقَّتِ السَّمَاءُ فَهِيَ يَوْمَئِذٍ وَاهِيَةٌ﴾ كَقَوْلِهِ: ﴿وَفُتِحَتِ السَّمَاءُ فَكَانَتْ أَبْوَابًا﴾ يَعْنِي: تَشَقُّقَهَا، وَالْوَاهِيَةُ: الضَّعِيفَةُ لَيْسَتْ فِي الشدَّة كَمَا كَانَت
