Laodicea was a wealthy city in Asia Minor. It had a problem with its water supply: the hot springs came from Hierapolis, several miles north, and the cold water came from Colossae, to the east. By the time either reached Laodicea through the aqueducts, it had arrived at the same temperature — lukewarm. Hierapolis's hot water was famous for its healing properties. Colossae's cold water was refreshing and clean. Laodicea's water was neither. It was tepid, mineral-laden, and made people physically ill.
When Jesus says "I will spue thee out of my mouth," the image to the church in Laodicea was immediate and visceral — they would have thought of their own water, the water that came in promising refreshment or healing and delivered neither. The rebuke is not against people who feel spiritually average. It is against a church that had the resources to heal and refresh others but had become so absorbed in its own wealth that it delivered nothing useful to anyone.
The context matters because it reframes the question. The problem Jesus identifies is not low emotional temperature — it is uselessness. The church in Laodicea thought it was rich and in need of nothing. Jesus says it is wretched, miserable, poor, blind, and naked. The self-assessment was entirely wrong. Lukewarm faith in this passage is not the faith of a person who is dry and struggling. It is the faith of a person who has stopped noticing they need anything.
Commentary is from a charismatic Protestant perspective, drawing on KJV text and public-domain sources including Spurgeon, Andrew Murray, and Matthew Henry.