By definition, a cult is a group or sect bound together by adoration of the same thing, person, ideal, etc.
A cult promises you redemption. It tells you that if you do what it says, and as it believes, you will be protected from the evil people that are out to get you and the rest of society.
A cult purges the non-believers. And it actively tries to vilify all those who are not part of the cult, saying that they're doomed and destined to go to hell.