Our nature, by the corruption of the first sin, is so deeply curved in on itself that it not only bends the best gifts of God toward itself and enjoys them (as is plain in the works-righteous and hypocrites), or rather even uses God himself in order to attain those gifts, but it also fails to realize that it so wickedly and viciously seeks all things, even God, for its own sake.
By the same steps [of idolatry] people even today arrive at a spiritual and more subtle idolatry, which is now quite common, by which God is worshiped, not as he is, but as he is imagined and reckoned to be. For ingratitude and love of vanity (that is, one’s sense of oneself and of one’s own righteousness, or, as they say, one’s good intention) violently blind people, so that they are incorrigible, and unable to believe otherwise than that they are acting splendidly and pleasing God. And in this way they form a God favorable to themselves, even though he really is not so. And so they more truly worship their fantasy than the true God, whom they believe to be like that fantasy.
– Martin Luther, as quoted in The End of Protestantism, p. 44.