Revolt against God
“Scripture identifies the essence of sin as ungodliness…God’s complaint is that we do not really ‘seek’ him at all, making his glory our supreme concern, that we have not set him before us, that there is no room for him in our thoughts, and that we do not love him with all our powers. Sin is the revolt of the self against God, the dethronement of God with a view to the enthronement of oneself. Ultimately, sin is self-deification, the reckless determination to occupy the throne which belongs to God alone.”
--John Stott, The Message of Romans, p. 100
"Sin...in addition to anything else it may be, is always an act of wrong judgement. To commit a sin, a man must, for the moment, believe that things are different from what they really are; he must confound values; he must see the moral universe out of focus; he must accept a lie as truth and see truth as a lie; he must ignore the signs on the highway and drive with his eyes shut; he must act as if he had no soul and was not accountable for his moral choices. Sin is never a thing to be proud of. No act is wise that ignores remote consequences, and sin always does. Sin sees only today, or at most, tomorrow; never the day after tomorrow, next month or next year. Death and judgment are pushed aside as if they did not exist and the sinner becomes for the time, a practical atheist who by his act denies not only the existence of God but the concept of life after death."
--A. W. Tozer, "There is No Wisdom in Sin," in Man: The Dwelling Place of God
"The truth is that evil is not a real thing at all, like God. It is simply good spoiled. . . . You know what the biologists mean by a parasite—an animal that lives on another animal. Evil is a parasite. It is there only because good is there for it to spoil and confuse."
--C. S. Lewis, They Stand Together: The Letters of C. S. Lewis to Arthur Greeves, p. 465.
Suicide of the Soul
“Sin is the suicidal action of the human will.”
--W. G. T. Shedd, “Sin is Spiritual Slavery,” in Sermons to the Natural Man