Whatever physical darkness is for the eyes, so is sin for the human soul. The spiritual darkness so darkens and blinds the eyes of the soul, that the sinner walks like the blind: he doesn't know where the path leads him; he doesn't see before him the torment of an eternal death in which he might fall; he doesn't distinguish vice from virtue, evil from good, truth from lies, true good fortune from evil fortune, and, thus, seeing he does not see and acts by touching like the blind.
Does he live in good fortune? He becomes violent, as an untrained and unrestrained horse, and does not see that with this good fortune God draws him to Himself as a father of a little child draws an apple. Will misfortune visit him? He grumbles, is indignant and blames, that as if he told a lie; he makes complaints and says a malicious word: "Am I a liar? In what have I sinned? Am I really more sinful than others? Am I worthy of this? Does my work deserve this?" He justifies himself, being full of every kind of untruth; he cleanses himself, being all besmirched; he considers himself unworthy of temporal punishment, but worthy of the eternal; he praises his merits, which stand for nothing.
All of creation, the heaven, the sun, the moon, the stars, the earth and its fulfillment, as if by mouth "tells of the glory of God" (Psalm 16:2); but the blind sinner does not feel the majesty of His glory and does not tremble. God, both through creation and by His word, reveals Himself for everyone; but the sinner, like a deaf person, does not hear His word and does not recognize the Lord. He hears the name of God, but he does not recognize God: he hears the voice of the Lord only with carnal instead of spiritual ears, and therefore, "hearing he does not hear and seeing he does not see".
When God is preached by His holy word, then His sacred will is also preached; but the sinner doesn't know it and does not make it his own. His omnipotence and majesty is preached, before which the sinner is not humble. His righteousness is preached before which the sinner is not afraid and does not honor. His truth is preached before which the sinner does not believe. His omnipresence is preached, before which the sinner does not show reverence. He does not show it because does not recognize Him. His most wise reason is preached, in which the sinner does not discern. His highest holiness is preached which the sinner does not honor. His supreme authority is preached which the sinner does not obey. His awesome glory is preached which the sinner does not honor. His timeless goodness is preached, in which the sinner makes no effort to participate. His fearful judgment is preached before which the sinner does not tremble, and so forth. Thus, the sinner is like "the man out of his mind who cannot know, and the stupid who cannot understand" (LXX Psalm 91:7) God and the acts of God.
And not only in relation to God, but also in relation to his neighbor, i.e. to any human, the blind man is a carnal and unenlightened man. We see that a person does evil to his neighbor, which he himself does not want; and does not do good to him, which he himself wants. We see that he is indignant and angry at the one who offends him; he abuses, abases, blames, discredits, lies about him, steals, kidnaps, takes away that which is his, and does other offenses; but he himself does such evil, or repays evil with evil, and is not ashamed and does not sense this. On the other hand, he wants his neighbor to be merciful to him and not leave him in need, for example: to quench his thirst and to give him drink when he thirsts, clothe the naked, welcome the stranger into his home and to comfort the sick and visit those in prison and do other works of mercy for him. All of this he wants, this truth is indisputable, but he himself does not want to do the same for a neighbor. We see that this evil is self-love, an untruth and blindness in Christians, who either silently pass by his neighbors living in misery as if not seeing them, or is ashamed to ask: "what can I do for him?" Many have plentiful food and a magnificent table for themselves, but do not care about a hungry neighbor; others wear all kinds of expensive clothes, and do not care about their naked neighbor; others build rich, large and tall houses and decorate the rest of the building, but for their neighbor who does not have a place to lay his head and to rest they do not care; they have silver, gold and other riches, comfortable for soul and life, that is kept whole and is saved, but there is no care for their neighbor who is burdened with debt and it is torment or prison for him for his shortfalls or sitting debts and suffering. We see this self-love and untruth in Christians: for not only they do evil, but also they don't do good for their neighbors, there is the untruth.
But, what it is even worse, we see that many Christians are not ashamed and are not afraid to steal, to kidnap and to be cunning, to flatter, to lie, to deceive, to slander, to scandalize, to denounce, to abuse, to commit adultery and make other offenses against their neighbor that they themselves would not want. All this comes from blindness.