So then because thou art lukewarm, and neither cold nor hot, I will spue thee out of my mouth. Because thou art lukewarm - Irresolute and undecided.
I will spue thee out of my mouth - He alludes here to the known effect of tepid water upon the stomach; it generally produces a nausea. I wilt cast thee off. Thou shalt have no interest in me. Though thou hast been near to my heart, yet now I must pluck thee thence, because slothful, careless, and indolent; thou art not in earnest for thy soul.