From the content of this letter to Pergamum we can conclude that this is largely a church comprised of Gentiles who have come out from Paganism.
When you come out of paganism and false religion you continue to face the pull of family, friends, and the world to draw you back in. Though you have become a new creature in Christ, the world you live in has not changed (home, work, neighborhood, friends, family, etc).
Every day you fight to keep believing the truth that is in Jesus Christ. The moment you let your guard down you may be drawn back in.
Sometimes the encouragement to go back into the past life comes from surprising places. Here in Pergamum there were teachers who encouraged compromise with false religions and unbiblical standards of morality.