﴿ 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 mountains feeling secure.