Revelation 2:14, "who taught Balak to throw a stumbling block before the children of Israel, to eat things sacrificed to idols, and to commit sexual immorality" - the sexual immorality Balaam's scheme produced.
Israel stayed in Shittim; and the people began to play the prostitute with the daughters of Moab;
But I have a few things against you, because you have there some who hold the teaching of Balaam, who taught Balak to throw a stumbling block before the children of Israel, to eat things sacrificed to idols, and to commit sexual immorality.
Balaam couldn't curse Israel through sorcery - not once in three tries. This chapter, coming right after, shows a different tactic succeeding where cursing failed: seduction into idolatry, from the inside, rather than a hired outside attack.