The parable of the Tares among the Wheat shows Satan’s imitation church growing up alongside the true Church. They appear very similar, but one has good fruit of the kingdom—and the other does not.
Pergamum is told to repent, or else the Lord will make war with them. But they are not left without promise. They are promised both sustenance and blessing, a white stone with a name known only to them.
Pergamum had compromised itself, mingling its members with the local pagan society. Like the trickery of Balaam, they were in danger of being destroyed from the inside out.
Pergamum was not a loveless church like Ephesus, nor did they face the strong persecution that Smyrna faced. Nevertheless, they are a compromised church. They hold tight to the name of Christ, but they have allowed a “stumbling block” to enter in among the flock.