“Can a blind man lead a blind man? Will they not both fall into a pit? A disciple is not above his teacher, but everyone when he is fully trained will be like his teacher.Why do you see the speck that is in your brother’s eye, but do not notice the log that is in your own eye? How can you say to your brother, ‘Brother, let me take out the speck that is in your eye,’ when you yourself do not see the log that is in your own eye? You hypocrite, first take the log out of your own eye, and then you will see clearly to take out the speck that is in your brother’s eye.”
(Luke 6:39-42 ESV)

The blind man is the the man without the gospel. If he tries to correct sin without first applying the gospel to his own life he will only make matters worse for himself and for others. Only when we apply the gospel to our own lives and find joy and fellowship with Jesus will we have the correct motives and power to help remove the speck from our brothers eye. With a forgiven gospel eye we become gracious worshipers of Jesus and friends of sinners.