It was only a few things and from only some within this otherwise good church.
“Nevertheless, I have a few things against you: There are some among you who hold to the teaching of Balaam, who taught Balak to entice the Israelites to sin so that they ate food sacrificed to idols and committed sexual immorality. Likewise, you also have those who hold to the teaching of the Nicolaitans. Repent therefore! Otherwise, I will soon come to you and will fight against them with the sword of my mouth.” (Revelation 2 v 14-16)
Whoever the Nicolaitans were, their teaching in the first century church was linked to that of the teaching of Balaam 6-7 centuries previously. It was the same age-old problem for the people of God. But there’s nothing new under the sun. A brief look at the story (Numbers 22-24) reveals how the prophet Balaam would not under King Balak’s orders curse the people of God. The donkey was blocked by an angel carrying a sword and Jesus says I have a sword in my mouth and I will fight against those who are destroying Pergamum church. Balaam has another idea and that is to entice the men of Israel with the Moabite women who were saying, ‘We worship our gods through eating this amazing food and having sex with these women, would you like to try?’ Jude (1:11) hints that there was financial gain for the Moabite women.
So the problem with this church was that it was being led astray from within by teaching which was seducing and enticing them away from Jesus into idolatry which are things we look to in order to find God, peace and satisfaction.
It may be difficult to see its application for us today. However even within the life of the Christian we can see idolatry of food, sex and money. Don’t idolise food. Consume food but don’t let food consume you. Don’t idolise sex. Sex doesn’t define you nor should it saturate your life. Don’t idolise money. Use money, save money, give money but don’t love money.
Churches/Christians may not be cursed today but they can be corrupted easily enough.