1 John defines sin as lawlessness. It then connects Jesus’ appearing with taking away sins. See 1 John 3:4–5.
In 1 John 3:4–7 the writer defines sin as “lawlessness” and links it directly to what has been made known about Christ. Christ appeared to take away sins and is himself without sin, so ongoing sinning is presented as incompatible with remaining in him. This unit sits in a section urging readers to live like God’s children and not be surprised by the world’s opposition (3:1–10). Just before this, the writer grounds moral seriousness in hope: those who look to Christ’s appearing purify themselves (3:2–3).
This paragraph ties the meaning of sin directly to Christ. Sin is not presented as a minor flaw but as “lawlessness”—a posture that runs against what God wants (explicit in verse 4). The writer then anchors ethics in shared teaching about Jesus: Christ “was revealed” to remove sins, and Christ himself is sinless (explicit in verse 5).
A careful answer keeps the immediate passage, the book's argument, and the whole-Bible storyline together, so the question is answered in context instead of as a detached idea.
Start with 1 John 3:4-5, then read the surrounding section so the answer stays connected to the passage's flow.
4Everyone who sins also commits lawlessness. Sin is lawlessness.
5You know that he was revealed to take away our sins, and in him is no sin.