"He is none of us" here signifies that he is not following the ways of Muslims. "The ways and traditions of the Days of Ignorance" means here wailing, i.e., `Alas! my lion, my moon, my support, one whose death has rendered his children orphan etc., etc.' This is a grave sin and there is a stern warning that one who does it, is in danger of losing his Faith because by doing so one, in fact, expresses resentment against Allah's Command.