What is a lukewarm Christian, and what is the difference between someone who is "lukewarm" and someone who is "hot" or "cold"?
The allusion refers to Christ's words to "the angel of the church of Laodicea" in Revelation. Christ said to John:
To the angel of the church in Laodicea write: "The words of the Amen, the faithful and true witness, the beginning of God's creation. I know your works: you are neither cold nor hot. Would that you were cold or hot! So, because you are lukewarm, and neither cold nor hot, I will spew you out of my mouth. For you say, I am rich, I have prospered, and I need nothing; not knowing that you are wretched, pitiable, poor, blind, and naked" (Rev. 3:14-17).
This is sometimes interpreted to refer to all of the faithful of Laodicea, but it is possible that Christ is speaking only of "the angel of the church," which is thought to be the head of that church, or the bishop. If so, then Christ may be saying that the bishop of the faithful in Laodicea is lukewarm. From the context, "lukewarm" means a condition of being neither antagonistic ("cold") or passionate ("hot") in the pursuit of his Christian duties. Rather, this Christian, perhaps the bishop, is self-satisfied with what he has, and evidently is unwilling to extend himself on behalf of Christ. Christ would rather he be cold or hot because antagonism or passion requires that someone cares. The hardest people to convert are not those who hate Christ but those who don't care about anything but their own satisfaction.