﴿ وَكَانُوا۟ يَنْحِتُونَ مِنَ ٱلْجِبَالِ بُيُوتًا ءَامِنِينَ ﴾

“notwithstanding that they had been wont [to enjoy Our blessings and] to hew out dwellings from the mountains, [wherein they could live] in security”

(And they used to hew out dwellings from the hills) from the mountains, (wherein they dwelt) secure) in the sense that they were safe from their collapse; it is also said that this means: safe from the torment.