No believer may belong to a false, or apostate, church for any reason whatsoever. No Christian may worship in or with a false church, whether as a member or as a mere “attender.” To do so is to make oneself responsible for the extreme wickedness of the false church of denying Christ, among many other evils…
When one sees that his or her church is becoming false, one should leave, if he or she cannot reform it.

Prof. David J. Engelsma