In the very first verse, we see that Jesus encountered a man born blind. This man had never seen a sunset, a rainbow, or the early morning sun. He had never seen his mother's face or his own reflection in a mirror. This man did not suffer from blindness because of a particular sin he had committed but his blindness was certainly the result of sin in general. The prevailing opinion in regard to sin today is that we shouldn't get to disturbed about it.
Some people say that sin is harmless.
However, we must realize that sin brings corruption, disease, destruction and death into our world. During Jesus' ministry, He cured a variety of needs. He healed the blind, the lame, and the demon-possessed. He brought a little boy back from the dead and returned him to his mother. There was no infirmity, no weakness, and no problem that Jesus could not heal.