Imagine having such a strong conviction about your own spiritual insight that you see yourself as a personal guide for others.
Paul is directly addressing the Jewish people here. They were highly confident, even proud, of their unique position as God's chosen people. They believed they possessed the Law and a special relationship with God, which they thought made them inherently superior and qualified to instruct the Gentile world.
This confidence wasn't just a casual thought; it was a deep-seated assurance that they were a 'guide to the blind' and a 'light to those in darkness.' They saw themselves as the enlightened ones, appointed to lead the ignorant masses (the Gentiles) toward truth and salvation.