C. S. Lewis and Others on the Nature of Sin

Psalm 51:3-5

For I know my transgressions, and my sin is ever before me. Against you, you only, have I sinned and done what is evil in your sight, so that you may be justified in your words and blameless in your judgment. Behold, I was brought forth in iniquity, and in sin did my mother conceive me.

Sin is described as "the plague of his own heart."

Matthew Henry comments on I Kings 8:38

Sin is the plague of our own heart; our indwelling corruptions are our spiritual diseases.

I Kings 8:38-39 NKJV

whatever prayer, whatever supplication is made by anyone, or by all Your people Israel, when each one knows the plague of his own heart, and spreads out his hands toward this temple: 39 then hear in heaven Your dwelling place, and forgive, and act, and give to everyone according to all his ways, whose heart You know (for You alone know the hearts of all the sons of men),

C. S. Lewis through Screwtape, the senior demon in the Screwtape Letters, points out the effectiveness of the smaller sins.

“You will say that these are very small sins; and doubtless, like all young tempters, you are anxious to be able to report spectacular wickedness. But do remember, the only thing that matters is the extent to which you separate the man from the Enemy. It does not matter how small the sins are provided that their cumulative effect is to edge the man away from the Light and out into the Nothing. Murder is no better than cards if cards can do the trick. Indeed the safest road to Hell is the gradual one-the gentle slope, soft underfoot, without sudden turnings, without milestones, without signposts.” (p. 56, Screwtape Letters)

Westminster Shorter Catechism

Q. 14. What is sin? A. Sin is any want of conformity unto, or transgression of, the law of God.

Scriptural Support for the Catechism Answer:

“If anyone sins, doing any of the things that by the Lord's commandments ought not to be done, though he did not know it, then realizes his guilt, he shall bear his iniquity. (Leviticus 5:17, ESV)

So whoever knows the right thing to do and fails to do it, for him it is sin. (James 4:17, ESV)

Everyone who makes a practice of sinning also practices lawlessness; sin is lawlessness. (1 John 3:4, ESV)

Jonathan Edwards on Sin

“Divines are generally agreed that sin radically and fundamentally consists in what is negative, or privative, having its root and foundation in a privation or want of holiness. And therefore undoubtedly, if it be so that sin does very much consist in hardness of heart, and so in the want of pious affections of heart, holiness does consist very much in those pious affections.” (Religious Affections)