"And to the angel of the church in Pergamos write; . . . I know thy works, and where thou dwellest, even where Satan's seat is: and thou holdest fast my name, and hast not denied my faith . . . But I have a few things against thee." (Revelation 2:12-14)
Retaining a clear identity as a church of the Lord Jesus in an evil environment is worthy of commendation. And indeed, this body of believers at Pergamos held fast to its Christian name--even in a city that was known (at least by God) as the place where Satan had his "seat." One of their members, Antipas, was killed for his faith. Yet the church at Pergamos remained faithful with a spiritual testimony, a small light in a sea of wickedness.
But perhaps because of the pressure surrounding them, the Lord warned them that they were allowing two destructive doctrines to flourish among them. The first was compromising with "wages of unrighteousness," exemplified by Balaam, which had become entrenched among the church (2 Peter 2:15). The second was the "doctrine of the Nicolaitanes," which their sister church in Ephesus also confronted (Revelation 2:15, 6).
Balaam was a well-known prophet who willingly accepted an assignment with an enemy of God's people so that he could receive a large sum of money (Numbers 22). And, even though God would not permit Israel to be cursed, as the enemy wanted, Balaam continued to promote his "error," and Israel lapsed into grave sin (Jude 1:11).
Not much is written in Scripture about the Nicolaitanes. The word basically means "conquer the people." This early teaching developed into a strong hierarchy of church polity over the next decades, and by the end of the second century, it was well established in the major cities. Jesus taught against such leadership (Matthew 20:26-27) and clearly said that He hated it (Revelation 2:6). HMM III