Conscience is a faculty of the mind, which, like every other, has suffered serious damage through our natural depravity, and it is by no means perfect. It is only the understanding acting upon moral subjects; and upon such matters it often puts bitter for sweet and sweet for bitter, darkness for light and light for darkness. Hence it is that men’s sins do not appear to them sin. In all probability there is not one, even among renewed men, who fully knows the evil of sin, nor will there be until in heaven we shall be perfect; and then, when we shall see the perfection of divine holiness, we shall understand how black a thing was sin. Men who have lived underground all their lives do not know how dark the mine is, nor can they know it until they stand in the blaze of a summer’s noon.

C.H. Spurgeon