First John 3:4 offers a very practical definition of the word “sin” – a sin is any action that falls outside the boundary of God’s will (including our thoughts, Acts 8:22, and our words, Matthew 12:36). While the KJV translates the last part of this verse as “…sin is the transgression of the law (from a root word meaning “to go over” a boundary), most other English translations use the word lawlessness – acting or being “without,” outside of what God allows. It is evermore important for Christians today to understand this very basic meaning of the word “sin,” simply because so many people in our society no longer believe in ANY kind of honest, objective standard of right and wrong. For many people today, “sin” is simply anything they dislike, anything of which they personally disapprove (but note the words of Solomon in Proverbs 21:2, “Every way of a man is right in his own eyes…”).
In verses 6-10 John illustrates in a clear, simple way how we can tell the difference between a “righteous” person and an “unrighteous” person – by looking at, “examining” what is the normal practice in that person’s life. One whose “default” behavior is faithful submission to God’s will (i.e., righteousness) – even though this person sometimes does stumble in sin (cf. Galatians 6:1) – is a righteous person, vs. 7. On the other hand, a person who routinely chooses evil over good is – even if they profess godliness, and at times do what is right – “of” the devil, vs. 8. (John’s words here expose the fallacy of those who contend for the “once saved, always saved” doctrine by trying to claim that the only alternative to their view must be that a Christian is “in” God’s grace only as long as they are not in the actual act of sinning and then totally “out” of His grace – and “absolutely lost” – the instant they succumb to any temptation. What the Holy Spirit shows us is that our God surveys the entirety of our lives as Christians, not only our condition in the moment.)
Echoing the essence of Jesus’ instruction to His disciples in John 13:34-35, John stresses the absolute necessity of love among Christians in 1 John 3:11-18. The example contrasting Cain’s rage in murdering his brother Abel because of his righteous works connects what John’s definition of sin with his explanation of righteousness and unrighteousness. Cain stands condemned not merely for the murder of his brother, but for the totality of his unrighteous actions (including his faulty sacrifice and his rebellious attitude about it), according to vs. 12. Had he loved as God desires, he would not have committed murder! John thus uses the presence of love of brethren in the Christian’s behavior as evidence that a person really has become the “new creature/new creation” Jesus wants them to be, vs. 14 (cf. 2 Corinthians 5:17). (In the example of Jesus offering Himself for us, vs. 16, John adds a “motivator” for Christians to imitate that degree of love toward one another.) Moving from concept to concrete, in vv. 17 -18 John stresses that love that is not practiced is not genuine love.