Everyone who makes a practice of sinning also practices lawlessness; sin is lawlessness. You know that he appeared in order to take away sins, and in him there is no sin. No one who abides in him keeps on sinning; no one who keeps on sinning has either seen him or known him. Little children, let no one deceive you. Whoever practices righteousness is righteous, as he is righteous. Whoever makes a practice of sinning is of the devil, for the devil has been sinning from the beginning. The reason the Son of God appeared was to destroy the works of the devil. No one born of God makes a practice of sinning, for God’s seed abides in him; and he cannot keep on sinning, because he has been born of God. By this it is evident who are the children of God, and who are the children of the devil: whoever does not practice righteousness is not of God, nor is the one who does not love his brother.
-1 Jno. 3:4-10, ESV
I read some passages in the Bible and when I try to identify the main idea, it sometimes seems to be the simple message that shouts to the reader: Don’t sin!
And our first response might be, “well I know that!” Then a deeper dive into the text will put on urgent display reasons to not sin. It seems to me that is true of this paragraph. If sin is lawlessness and Jesus appeared to take it away; if I sin and keep on sinning, I no longer abide in Christ; if sin is “of the devil,” and righteousness is made possible by Christ; if I am really a child of God – when sin approaches my attitude will be: “I can’t do that!”
Then John gives one example, that transitions into the next section. “Whoever does not practice righteousness is not of God, nor is the one who does not love his brother.”
Note also, “cannot keep on sinning” doesn’t mean we are incapable of sinning, it means our aim/purpose is to not sin. Again, when sin approaches my attitude should be, “I can’t do that!”