Importance of rational thought in faith

بَلْ قَالُوٓا۟ إِنَّا وَجَدْنَآ ءَابَآءَنَا عَلَىٰٓ أُمَّةٍ وَإِنَّا عَلَىٰٓ ءَاثَـٰرِهِم مُّهْتَدُونَ

Rather, they say, "Indeed, we found our fathers upon a religion, and we are in their footsteps [rightly] guided."