2:14 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.
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
Why should this be so bad? If a person could eat things sacrificed to idols this may indicate that one tolerates (or even worships) these idols. God is a very jealous God. He will not have ANY god before Him (Exodus 20:3).
The teachings of Balaam was that it was alright to intermarry with heathen and compromise over idolatrous worship. We can see this in Numbers chapters 22 through 25.
At the time of Revelation's writing, men indulged in sexual intercourse with temple priestesses in cult prostitution. Even if this phrase didn't refer to temple prostitution but rather to spiritual unfaithfulness, this, too, is not right in God's sight. See Ezekiel 23:36-39. It is so easy to follow the advise of "friends" or because "they are doing it..." makes the immorality OK. Not so. John tells us earlier in his life, 1 John 5:18-21, that we are to guard ourselves from idols.