However, St. John says that anyone who hates his brother is "still in darkness" even though he may say he is "in the light". In context, that means someone who thinks he's infallibly "once saved always saved" but hates his brother is on his way to hell, no matter how "born again" he thinks he is.
Let him who has ears hear ...
Perhaps it would have been more clear if I had said "I'd say that that hatred is a sin."