You saying once saved, always saved doesn't apply? What about those who have personalities that are such that they are cruel instead of loving in their relationships with people, or overly controlling. Those too qualify as sins, are usually knowingly and habitually committed, yet are overlooked by the church.
If you knowingly, willfully, blatantly, habitually commit sin...and you feel no remorse, no grief, no sorrow, and have no conviction about that sin...then you have NO reason whatsoever to believe that you are a Christian. You had better repent and get saved.
John is teaching this in his epistle.