To dream that you are in a cult, suggests that you are in some destructive and/or manipulative relationship. You are being exploited. On a more positive note, you have the desire to strive for a better Self. It implies devotion and sense of community.
To see a cult in your dream, indicates that you are lacking any spiritual freedom.
To dream that you are a leader of a cult, signifies your authoritarian attitude. No one should question your motives or choices.
An attempt for power or control over others, possibly to feed the controller's ego, insecurity, or low-self esteem, or feelings of helplessness
Manipulation
Being misleading, purposely or otherwise
The idea of buying into an illusion, being "sucked in," or tricked
The idea of changing one's beliefs to serve some other purpose (such as to feel more accepted, spiritual, etc.