The Jews are blind as to whom the true Messiah is. They are looking for the Messiah even as they bow at the wailing wall. They not only refuse to believe that Christ has come, they also hate the Christ of the Scriptures. Until their eyes are opened they will still refuse to believe. The sign miracle may have as its main emphasis a lesson to the Jew.
Spiritual blindness is universal.
No person apart from Jesus has been born without this condition. Never have I looked upon a blind person without a certain degree of pity and with a great heart of thanksgiving at my own ability to see. My father was blind. Though he was not born blind, he suffered blindness for almost the last thirty years of his life. He had two cornea transplants and eventually lost most of his sight to blood vessels that ruptured in his eyes.