Revelation 2:14-16

Revelation 2:14: “But I have a few things against thee, because thou hast there them that hold the doctrine of Balaam, who taught Balac to cast a stumblingblock before the children of Israel, to eat things sacrificed unto idols, and to commit fornication.
15 So hast thou also them that hold the doctrine of the Nicolaitanes, which thing I hate.”

The Lord had a few things against the church at Pergamos, but to understand the issues we need to do some research. The story of Balaam can be found in the Old Testament. Balak, king of the Moabites, hired Balaam to curse Israel because Balaam had a peculiar gift: whoever he blessed was blessed, and whoever he cursed were cursed. Balaam went out to curse Israel, but God intervened and Balaam blessed them instead. However, after this Balaam told Israel’s enemies how they could coax God into cursing Israel, and based on his advise they sent Midian women into the camp to commit fornication with the Israelites. God cursed Israel for this – but He also cursed Balaam. This is why the verse says that Balaam “taught Balac to cast a stumblingblock before the children of Israel”. Balaam did it for the reward that it brought, but God was not pleased about it.

What it boils down to is this: Balaam corrupted God’s people through intermarriage with pagans in order to get them to commit fornication and idolatry. This is what was happening to the church in the days of Constantine. When the pagan state essentially “married” the church, joining the two together, the intermarriage corrupted the church and brought in spiritual adultery, pagan practices, and idolatry. This is the “doctrine of Balaam”. God had a strict warning for them:

Revelation 2:16: “Repent; or else I will come unto thee quickly, and will fight against them with the sword of my mouth.”

The Lord commanded the church to repent, or else He would fight them with the Word.