"The example of those who take allies other than Allah"—meaning: their idols which they worshipped instead of Allah—"is like the spider that takes a house. And indeed the weakest of houses"—the weakest of dwellings—"is the house of the spider." That is: their idols do not avail them anything, just as the spider's web provides no shelter from heat or cold. "If they only knew"—they would have known that their idols do not avail them anything.
﴿مثل الَّذين اتخدوا من دون الله أَوْلِيَاء﴾ يَعْنِي: أَوْثَانَهُمُ الَّتِي عَبَدُوهَا مَنْ دُونِ اللَّهِ ﴿كَمَثَلِ الْعَنْكَبُوتِ اتَّخَذَتْ بَيْتا وَإِن أوهن الْبيُوت﴾ أَضْعَف الْبيُوت ﴿لبيت العنكبوت﴾ أَيْ: إِنَّ أَوْثَانَهُمْ لَا تُغْنِي عَنْهُمْ شَيْئًا كَمَا لَا يَكِنُّ بَيْتُ الْعَنْكَبُوتِ مِنَ حَرٍّ وَلَا بَرْدٍ ﴿لَوْ كَانُوا يَعْلَمُونَ﴾ لَعَلِمُوا أَنَّ أَوْثَانَهُمْ لَا تُغْنِي عَنْهُم شَيْئا