The use of contrasts can be a powerful artistic technique. By bringing together two sharply different colors or by juxtaposing two radically opposite images, the artist can jolt the viewer into paying attention, and a writer can alert a reader to key point.
The use of contrasts works in our text today as well. Yesterday’s focus on the life and identity of God’s children is reinforced but also contrasted with the life and identity of the “children of the devil” (v. 10). The two are radical opposites.
John emphasizes again the new nature of God’s children. Those who abide in Christ do not “keep on sinning” (v. 6). They do not “continue to sin;” in fact, they “cannot go on sinning” (v. 9). Scripture is clear: a life in Christ means a transformed life. This does not mean Christians are now perfect people who never sin; we’ve already seen the remedy for that sin described (1:9; 2:1–2). It does mean that the Christian life should be notable for its purity and resistance to sin.
In contrast, “children of the devil” have an entirely different ethos. They continue in sin unchecked. They do not “do what is right,” nor do they “love their brother and sister” (v. 10). Their lives embody the habits of sin, hatred, and disobedience rather than purity, confession, and love. Scripture makes the reason clear: “The one who does what is sinful is of the devil, because the devil has been sinning from the beginning” (v. 8). They are simply imitating the one to whom they belong. Do not miss the point of the contrasts: “This is how we know who the children of God are and who the children of the devil are” (v. 10).