‘I know your works, that you are neither cold not hot. I would you were cold or hot. So because you are lukewarm, and neither hot nor cold, I will spew you out of my mouth.'
Laodicea's water supply came from hot springs piped down from five miles away so that by the time it reached them it was lukewarm. They knew by experience the problems caused by lukewarm water and its effect on the digestive system. So Jesus describes them as like lukewarm water that can only make someone sick.
Many Bible students misunderstand this idea. It does not mean that the Laodiceans were only semi-spiritual, half and half, and that He would prefer them even to be unspiritual. The idea was rather that because they were like lukewarm water they were useless for anything, and could only make people vomit. Cold water had its uses and so did hot water, but lukewarm water had none. It just made men sick. And so did they.
They were self-satisfied, complacent and unresponsive. They were so self-important that they felt they were doing enough when in reality they were doing nothing of any real importance at all, nothing that counted. They were lacking in every way, but were so proud that they did not realise their own inadequacy. There is no mention of their love for Christ, or of their faith, or of their endurance, or of their works. They did not get involved. They just sat and preened themselves.
Jesus was not wishing that they were either fully spiritual or not spiritual at all, He was wishing that they had some value, like cold water for drinking or hot water for bathing. A lukewarm, useless Christian, who can only make people sick, is a contradiction in terms.
‘I will spew you out of my mouth'. These words have in mind Leviticus 18:25; Leviticus 18:28; Leviticus 20:22 where the inhabitants of Canaan are to be vomited out because of their sexually evil ways, and Israel is warned that for similar behaviour they too will be vomited out. However there is no mention of any particularly bad sexual irregularity here, so that it is the general idea that is taken up and probably their overweening pride and spiritual uselessness that made Jesus sick.