The word lukewarm is only used once in the Bible, the famous Revelation 3:16, where Jesus tells the church at Laodicea that their deeds are neither hot nor cold so he will spit (literally vomit) them out of his mouth. The Greek work for lukewarm is chliaros, which is actually more like “wildly fluctuating between extremes,” or unstable. Jesus is rebuking these rich, lazy, luxury-dependent Laodiceans for their inconsistency.