"I know your works, that you are neither cold nor hot. I wish you were cold or hot. So, because you are lukewarm, and neither hot nor cold, I will vomit you out of my mouth"
It is thought that the Laodiceans were being criticized for their neutrality or lack of zeal (hence "lukewarm"). Based on this understanding, the pejorative term Laodicean is used in the English language to refer to those neutral or indifferent in matters of faith.
However, some scholars have suggested that this metaphor has been drawn from the water supply of the city, which was lukewarm, in contrast to the hot springs at nearby Hierapolis and the pure water of Colossae (Barclay). The archaeology shows Laodicea had an aqueduct that probably carried water from hot mineral springs some five miles south, which would have become tepid before entering the city
The imagery of the Laodicean aqueduct suggests not that "hot" is good and "cold" is bad, but that both hot and cold water are useful, whereas lukewarm water is useless.
Barclay, William, Letters to the Seven Churches, Edinburgh, 1957 (reprinted 2001).