As i'm reading through "Holiness" by J. C. Ryle as part of Tim Challies 'Reading Classics Together' I can't resist the urge to post some of what Ryle says. So here's some extracts in which Ryle defines 'sin', taken from the 1st Chapter; Sin
"Sin," speaking generally, is, ... ..."the fault and corruption of the nature of every man that is naturally engendered of the offspring of Adam; whereby man is very far gone from original righteousness, and is of his own nature inclined to evil, so that the flesh lusts always against the spirit; and, therefore, in every person born into the world, it deserves God’s wrath and damnation."
Sin is that vast moral disease which affects the whole human race, of every rank and class and name and nation and people and tongue, a disease from which there never was but one born of woman that was free. Need I say that One was Christ Jesus the Lord?
I say, furthermore, that "a sin," to speak more particularly, consists in doing, saying, thinking or imagining anything that is not in perfect conformity with the mind and law of God. "Sin," in short as the Scripture says, is "the transgression of the law" (1 John 3:4). The slightest outward or inward departure from absolute mathematical parallelism with God’s revealed will and character constitutes a sin, and at once makes us guilty in God’s sight.
...a man may break God’s law in heart and thought when there is no overt and visible act of wickedness. Our Lord has settled that point beyond dispute in the sermon on the mount (Matt. 5:21–28).
Again, I need not tell a careful student of the New Testament, that there are sins of omission as well as commission, and that we sin, as our Prayer Book justly reminds us, by "leaving undone the things we ought to do," as really as by "doing the things we ought not to do." The solemn words of our Master in the Gospel of St. Matthew place this point also beyond dispute. It is there written: "Depart . . ., you cursed, into everlasting fire . . . for I was an hungry, and you gave Me no meat: I was thirsty, and you gave Me no drink" (Matt. 25:41, 42).
It [sin] is not picked up from bad companions and bad examples, as some weak Christians are too fond of saying. No! It is a family disease, which we all inherit from our first parents, Adam and Eve, and with which we are born. Created "in the image of God," innocent and righteous at first, our parents fell from original righteousness and became sinful and corrupt. And from that day to this all men and women are born in the image of fallen Adam and Eve and inherit a heart and nature inclined to evil. "By one man sin entered into the world." "That which is born of the flesh is flesh." "We are by nature children of wrath." "The carnal mind is enmity against God." "Out of the heart [naturally, as out of a fountain] proceed evil thoughts, adulteries" and the like (Rom. 5:12; John 3:6; Eph. 2:3; Rom. 8:7; Mark 7:21).