1 John / Question
The letter says the distinction is shown by practice: whoever does not practice righteousness is not of God, and neither is the one who does not love a brother. It presents behavior as the identifying evidence. See 1 John 3:10.
In 1 John 3:8–10 the writer draws a sharp line between two “families,” identified by ongoing behavior. Ongoing sinning aligns a person with the devil, whose pattern has existed “from the beginning.” The Son of God appeared with the purpose of undoing the devil’s works. This unit sits inside a larger section that describes what it looks like to be “children of God” in everyday life (roughly 1 John 2:28–4:6). Just before it, the writer urges purity in light of future hope and begins contrasting sin with Christ’s appearing (3:3–7).
The passage presents two “families” that show themselves through recognizable patterns of life.
A common mistake is to turn the wording into a slogan. The better reading keeps the phrase tied to the passage, the speaker, and the problem the book is addressing.
Start with 1 John 3:10, then read the surrounding section so the answer stays connected to the passage's flow.
10In this the children of God are revealed, and the children of the devil. Whoever doesn’t do righteousness is not of God, neither is he who doesn’t love his brother.