"Nay, they said: We found our fathers upon a religion," meaning a creed, which is the creed of polytheism, "and we are guided by their tracks," meaning: they were upon guidance and we are following them upon that guidance.
﴿بَلْ قَالُوا إِنَّا وَجَدْنَا آبَاءَنَا على أمة﴾ مِلَّة , وَهِي ملَّة الشّرك ﴿وَإِنَّا على آثَارهم مهتدون﴾ أَي: أَنهم كَانُوا على هدى وَنحن نتبعهم على ذَلِك الْهدى ,