"I know where you live -- where Satan has his throne. Yet you remained true to my name. You did not renounce your faith in me..." (2:13)*.
Yet, you have people who teach Balaam (see Numbers chapter 25 and 31:16) and others who hold to the teaching of the Nicolaitans**.
"Repent..." (2:16). "...To him who overcomes, I will give some of the hidden manna. I will also give him a white stone with a new name written on it, known only to him who receives it." (2:17)***.
*It is believed that Pergamum was the center for a number of different forms of idol worship. Thus it is said, it is "where Satan has his throne." Choosing where to live can be very important! In some cases refusal to worship meant death; perhaps somewhat like in Daniel chapters 3 and 6.
**It is thought the Nicolaitans were a sect who advocated licentiousness (unrestrained sexual activity) as the proper way of life.
***Hidden manna maybe the fruit of the tree of life in (22:2) for the healing of the nations. Again, see the connection between repentance and healing (forgiveness)! The white stone maybe the pure, sure knowledge of the Word of God written in the mind of those who overcome, see Ezekiel 3:9.