"Rather, we follow what we found"—meaning: what we discovered—"our forefathers doing. Even if their forefathers did not understand anything nor were guided?" [And if they were guided, they would not have followed them].
﴿بل نتبع مَا ألفينا﴾ أَي: وجدنَا ﴿عَلَيْهِ آبَاءَنَا أَوَلَوْ كَانَ آبَاؤُهُمْ لَا يَعْقِلُونَ شَيْئًا وَلَا يَهْتَدُونَ﴾ [وَلَو كَانُوا مهتدين مَا اتَّبَعُوهُمْ].