It is certain that man never achieves a clear knowledge of himself unless he has first looked upon God’s face, and then descends from contemplating him to scrutinize himself. For we always seem to ourselves righteous and upright and wise and holy—this pride is innate in all of us—unless by clear proofs we stand convinced of our own unrighteousness, foulness, folly, and impurity. Moreover, we are not thus convinced if we look merely to ourselves and not also to the Lord, who is the sole standard by which this judgment must be measured.
For, because all of us are inclined by nature to hypocrisy, a kind of empty image of righteousness in place of righteousness itself abundantly satisfies us. And because nothing appears within or around us that has not been contaminated by great immorality, what is a little less vile pleases us as a thing most pure—so long as we confine our minds within the limits of human corruption. Just so, an eye to which nothing is shown but black objects judges something dirty white or even rather darkly mottled to be whiteness itself.
John Calvin, Institutes of the Christian Religion & 2, ed. John T. McNeill, The Library of Christian Classics, (Louisville, KY: Westminster John Knox Press, 2011), 1:37–38.