Revelation 3:15

Amplified Bible

¹⁵‘I know your deeds, that you are ^[a]neither cold (invigorating, refreshing) nor hot (healing, therapeutic); I wish that you were ^[b]cold or hot.

Revelation 3:15 This phrase and the word lukewarm in v 16 form a metaphor that is probably based on the quality of the water supply of Laodicea, which was delivered by aqueduct from the hot mineral springs about five miles away. During its journey, the water cooled to a warm or lukewarm temperature.
Revelation 3:15 I.e. alive, productive—beneficial in one way or the other.