What Exactly Is Sin, Anyway?

Question: I’ve heard over and over that Jesus Christ was crucified because of sin. But what exactly is sin?

Answer: It may not be a word that most people think much about, but God did indeed give His only begotten Son, Jesus Christ, to suffer an excruciatingly painful death so that everyone in the world could be forgiven and cleansed of sin. Obviously, then, it is important to know what sin is.

Let’s see what the Bible says—because even though the human mind has produced a lot of wild ideas about what sin is, the Bible gives a clear and simple definition. Once we know that definition, we can build on it with what Jesus Christ taught. The clearest biblical definition is found in 1 John 3:4, which says, “Whoever commits sin also commits lawlessness, and sin is lawlessness.” The King James Version provides a little more clarity: “Whosoever committeth sin transgresseth also the law: for sin is the transgression of the law.”

In other words, sin is the violation—the breaking—of the law. But what law? This is clearly not referring to any civil laws outside of the Bible. Neither is it referring to the hundreds of additional laws prescribed by Jewish authorities over the years, which Jesus Himself condemned. So, what law is it talking about?

The Bible gives the answer. James, one of Jesus’ half-brothers, makes it clear: “He who said, ‘Do not commit adultery,’ also said, ‘Do not murder.’ Now if you do not commit adultery, but you do murder, you have become a transgressor of the law” (James 2:11). Clearly, “the law” that is referred to here means the Ten Commandments. Elsewhere in Scripture, the Apostle Paul said, “I would not have known sin except through the law. For I would not have known covetousness unless the law had said, ‘You shall not covet’” (Romans 7:7). This, again, is directly from the Ten Commandments.

The Bible’s primary definition of sin is the breaking of the Ten Commandments. Of course, the Bible also shows that sin includes showing partiality (James 2:9), not doing good (James 4:17), a proud heart (Proverbs 21:4), acting against faith (Romans 14:23), and various other offenses—but these New Testament applications flow from the Ten Commandments, which form the core of God’s law, and all sin can ultimately be found to violate one or more of the Ten Commandments.

Sin Begins in the Mind

Building on this idea, Jesus explained that sin is not just physically breaking one of the Ten Commandments—rather, there is an even deeper, spiritual component. He said, “You have heard that it was said to those of old, ‘You shall not commit adultery.’ But I say to you that whoever looks at a woman to lust for her has already committed adultery with her in his heart” (Matthew 5:27–28).

So, it isn’t just the physical act of adultery that constitutes sin—sin occurs when lustful thoughts enter the mind. This also applies to murder; Christ taught that even an attitude of hatred violates the spirit—the full intent—of the law, putting the sinner in danger of judgment (Matthew 5:21–22). Jesus taught that sin begins in the mind. We read that “when desire has conceived, it gives birth to sin; and sin, when it is full-grown, brings forth death” (James 1:15).

Again, the primary biblical definition of sin is the breaking of the Ten Commandments. We sin whether we break the letter or the spirit of the law by our actions, words, thoughts, or even wrong motivations. And, at some point, all of us have broken one or more of the Ten Commandments, at least in the spirit of the law. This is why we read that “all have sinned and fall short of the glory of God” (Romans 3:23), and this is why we need the sacrifice of Jesus Christ to cover our sins—because even though we are told to repent and turn away from sin, all the obedience in the world cannot make us right with God for our past sins. Only “the blood of Jesus Christ His Son cleanses us from all sin” (1 John 1:7).