The person who practices sin belongs to the devil, because the devil has been sinning since the beginning. God's Son appeared for this purpose: to destroy the works of the devil.
Those born from God don't practice sin because God's DNAa remains in them. They can't sin because they are born from God.
This is how God's children and the devil's children are apparent: everyone who doesn't practice righteousness is not from God, including the person who doesn't love a brother or sister.