John 12:40,41

He hath blinded their eyes, and hardened their heart.

This explains why they could not believe. Whether they were morally responsible for their unbelief depends on how God blinded their eyes and hardened their heart. If he did it by. direct act, regardless of their moral condition, then they were not responsible. If, however, he did it by. law of the universe that whoever turns from the light shall become blind, and whoever steels his heart against the truth shall find his heart hardened, then they were morally responsible if they had turned from the light and hardened their hearts. It is. physical as well as. moral law that he who turns from the light and seeks to abide in darkness will become blinded until he will "believe. lie and be damned." The men who are the champions of unbelief, such men as Voltaire, Paine and Ingersoll, are unbelievers because they did not wish to believe. Their moral condition was such that they could justify their course of life only by refusing to believe on Christ. They sought the darkness, and as. result, finally they became so blinded that they could not believe. They blinded their own eyes because they brought upon themselves the penalty. God blinded their eyes, because their blindness resulted from the action of his universal law. Thus it is said of Pharaoh that "God hardened his heart," but it is also said that "Pharaoh hardened his heart." He chose, in the exercise of his voluntary agency, to harden his heart, but it is God's law that those who harden their hearts shall be hardened, and hence God, by this law, hardened his heart. By reference to Matthew 13:14 the reader will find this passage from Isaiah quoted and applied by the Savior to the Jews. In the application he shows how they were blinded: "Their eyes have they closed." The Savior's words settle how God blinded their eyes. It was by the application of his invariable law to their own acts. Trench says: "The Lord, having constituted as the righteous law of moral government, that sin should produce darkness of heart and moral insensibility, declared that he would allow the law to take its course."