We have nearly lost the word. “Sin” survives mostly as a joke on dessert menus — a chocolate cake is “sinfully” rich — or as a relic people associate with scolding and shame. So before we can answer what sin is, we have to recover the seriousness of the question, because everything else in the Christian message hangs on it. If sin is trivial, then the cross is an overreaction. If sin is what the Bible says it is, then the cross is the most necessary and most beautiful thing that ever happened. You cannot understand grace until you understand the thing grace answers.
So let me give you the plain biblical answer, without flinching from it and without piling on more weight than Scripture does. Sin is real, it is universal, it is serious — and it is, thank God, not the last word.
Sin: missing the mark, breaking the law
The Bible has two main pictures for sin, and they fit together. The first is legal — sin as the breaking of God’s law:
Whosoever committeth sin transgresseth also the law: for sin is the transgression of the law. 1 John 3:4
God is not an arbitrary rule-maker; His law is a description of His own character and of how the world He built actually works. To break it is not to trip over a technicality but to act against the grain of reality and against the One who loves you. The second picture is the one buried in the very word the New Testament most often uses for sin — hamartia, an archer’s term meaning to miss the mark. Picture an arrow aimed at a target and falling short, or veering wide. That is sin: not merely doing wicked things, but missing what we were made for. Paul puts both ideas in a single, leveling sentence:
For all have sinned, and come short of the glory of God; Romans 3:23
Come short of the glory of God. We were made to reflect God — to bear His image, to live in love and truth and holiness — and we have all fallen short of it. Notice the word all. This is not a category for criminals and tyrants while the rest of us watch from the stands. The kindest person you know has come short of the glory of God. So have I. So have you. That universality is not the Bible being harsh; it is the Bible being honest about something every clear-eyed person already suspects.
The sins we do and the sins we don’t
We tend to think of sin only as committing forbidden acts — lying, stealing, cruelty, lust. Those are real, and Scripture names them plainly. But the Bible is just as concerned with the good we fail to do:
Therefore to him that knoweth to do good, and doeth it not, to him it is sin. James 4:17
This is why no one can hide behind “I never hurt anybody.” The man who walks past the wounded traveler has broken no commandment by his action — he simply did nothing. And Jesus said that doing nothing, when love required something, is itself a failure of love and therefore sin. So sin comes in two forms: the wrong we commit and the right we omit. Once you see both, the comfortable hope that you are basically fine grows very thin. The standard is not “avoid the worst”; the standard is love — whole-hearted love of God and neighbor — and none of us has kept it. This, by the way, is exactly what the Ten Commandments were given to expose.
Sins are symptoms; sin is the disease
Here is the deeper thing, and it is where the Bible parts company with every self-improvement scheme. Behind the sins — plural, the acts — lies sin, singular: a condition, an orientation of the heart. We do not sin merely because we are badly taught or poorly raised; we sin because something in us is bent inward, set on being our own god. Isaiah names it with a perfect image:
All we like sheep have gone astray; we have turned every one to his own way; and the LORD hath laid on him the iniquity of us all. Isaiah 53:6
We have turned every one to his own way. That is the essence of it — not this or that misdeed, but the deep preference for my way over God’s, the quiet treason of the self on the throne. Jesus located sin in the heart, not merely the hands: it is “out of the heart” that evil thoughts and deeds proceed. This is why behavior modification can never finally cure it. You can prune the visible branches of a poisonous tree and it will keep producing poison, because the trouble is in the root. Sin is the disease; sins are the symptoms. And a remedy that treats only symptoms is no remedy at all.
Why sin is so serious
People often feel the Bible overstates the problem. Surely God grades on a curve? But weigh what sin actually is — treason against an infinitely good God, the spoiling of His image in us, the source of nearly every human misery from broken homes to broken nations — and the Bible’s seriousness starts to look like simple accuracy. Sin always costs. It costs now, in the wreckage it leaves, and it costs ultimately:
For the wages of sin is death; but the gift of God is eternal life through Jesus Christ our Lord. Romans 6:23
Read that verse slowly, because it holds the whole gospel in miniature. Wages — what sin earns, what it has coming, what is owed: death, separation from the God who is the source of all life. That is the bad news stated at full strength. But the sentence does not stop at the semicolon. But the gift of God — and now everything turns. Over against wages we have earned stands a gift we could never earn, and that gift is life, and it comes through one Person. Which is why I keep insisting the bad news about sin exists for the sake of the good news. You do not tell a healthy man he needs a cure.
The only remedy that reaches the root
If sin were only behavior, the answer would be better behavior. But sin is a condition of the heart and a debt against God, so the answer has to do two things no self-help program can: it has to pay the debt and change the heart. That is precisely what God provided in Christ. On the cross, the iniquity that was ours was laid on Him — the second half of Isaiah’s verse: the LORD hath laid on him the iniquity of us all. He took the wages so that we could receive the gift. That is why we call it grace. I have written the whole of it in Why Did Jesus Have to Die? and What Is the Gospel?, and I would point you there next, because the answer to “what is sin?” is only half a sentence until you reach “and here is what God did about it.”
What does this ask of you today? Two things, really. First, stop minimizing it. Do not call your sin a mistake, a slip, a personality quirk; call it what God calls it, because only honest people can be forgiven — the man who insists he is healthy will never go to the Physician. Second, turn. The biblical word is repentance: agreeing with God about your sin and turning from your own way back to His. And when you turn, you will find that He is not waiting to condemn you but running to receive you. If we confess our sins, he is faithful and just to forgive us our sins, and to cleanse us from all unrighteousness (1 John 1:9). That is what grace means. The point of seeing your sin clearly is never to leave you in despair. It is to send you, at last, to the only One who can take it away.