Acts 6 mentions 'Nicolas, a proselyte from Antioch.' Writings of the time say he later came to follow Gnostic teachings and became an ascetic.
The end-time church is warned against Nicolaitanism, for it exists today. The Scriptures, plus some first century history, reveal who the Nicolaitans are.
The vast majority of Christian-professing churches has been saturated with pagan doctrines (like antinomianism and dispensationalism), derived from Gnosticism.
The early church was invaded by Gnosticism that denigrated the 'enslavement to Yahweh, His Law, and the Sabbath,' replacing it with Greek philosophy.
Cultural compromise, such as found in Pergamos, brings judgment from Jesus. To those who refuse to compromise their convictions, Christ promises eternal life.
The Ephesus church effectively battled various heresies, for which Christ commends it. However, the members lost sight of the reason, having left their first love.