Knowledge of the Holy by A. W. Tozer

The natural man is a sinner because and only because he challenges God’s selfhood in relation to his own. In all else he may willingly accept the sovereignty of God; in his own life he rejects it. For him, God’s dominion ends where his begins. For him, self becomes Self, and in this he unconsciously imitates Lucifer, that fallen son of the morning who said in his heart, “I will ascend into heaven, I will exalt my throne above the stars of God. . . . I will be like the Most High.”
Yet so subtle is self that scarcely anyone is conscious of its presence. Because man is born a rebel, he is unaware that he is one. His constant assertion of self, as far as he thinks of it at all, appears to him a perfectly normal thing. He is willing to share himself, sometimes even to sacrifice himself for a desired end, but never to dethrone himself. No matter how far down the scale of social acceptance he may slide, he is still in his own eyes a king on a throne, and no one, not even God, can take that throne from him.
Sin has many manifestations but its essence is one. A moral being, created to worship before the throne of God, sits on the throne of his own selfhood and from that elevated position declares, “I AM.” That is sin in its concentrated essence; yet because it is natural it appears to be good. It is only when in the gospel the soul is brought before the face of the Most Holy One without the protective shield of ignorance that the frightful moral incongruity is brought home to the conscience. In the language of evangelism the man who is thus confronted by the fiery presence of Almighty God is said to be under conviction. Christ referred to this when He said of the Spirit whom He would send to the world, “And when he is come, he will reprove the world of sin, and of righteousness, and of judgment.”