It is true that for many people much remains abstruse; but this is not due to the obscurity of Scripture, but to the blindness or indolence of those who will not take the trouble to look at the very clearest truth. It is as Paul says of the Jews in II Corinthians [3:15]: “A veil lies over their minds”; and again: “If our gospel is veiled, it is veiled only to those who are perishing, whose minds the god of this world has blinded” [II Cor. 4:3 f.]. With similar temerity a man might veil his own eyes or go out of the light into the darkness and hide himself, and then blame the sun and the day for being obscure. Let miserable men, therefore, stop imputing with blasphemous perversity the darkness and obscurity of their own hearts to the wholly clear Scriptures of God.
The Bondage of the Will
Luther’s Works Vol. 33