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.