Laodicea: cold or hot

The city of Laodicea had no good spring of its own and got its drinking water through an aqueduct. Nearby Hierapolis had hot springs, good for healing. Colossae was known for cold, fresh water. Many interpreters think the water reached Laodicea lukewarm, though archaeologists aren't sure of that.

On that reading, the image works like this: hot water heals, cold water refreshes. Lukewarm water does neither, and you spit it out. In that case, it isn't about zeal or feelings, but about what the church means to others.