See commentary on Revelation 2:2.
ψυχρὸς [psychros] : in mind: of one destitute of warm Christian faith and the desire for holiness.1
ζεστός [zestos] , used of boiling water.2
I could wish
It is always and constantly Gods desire that men would fear Him and keep His commandments, but men still choose to walk in their own counsels (Deu. Deu. 5:29; Ps. Ps. 81:10-13).
you were cold or hot
Here we have what would seem to be an allusion to the marginal water supply of Laodicea:
Rudwick and Green emphasize that the site of Laodicea was chosen for its position at an important road-junction. It lacked a natural water-supply, for there are no springs on the site, and the Lycus River dries up in summer (p. 177). The remains of a remarkable aqueduct of stone pipes indicate that the people derived water from a source south of the city, perhaps from the hot mineral springs near Denizli, the modern town five miles distance. This would have cooled only slowly in the pipes, and on arrival the supply would have been tepid and its effect emetic.3
The people of Laodicea had built an aqueduct to supply their city, but the water was lukewarm and impure. The remains can still be seen, and thick deposits of calcium carbonate inside the pipes witness plainly to the worth of the water which once flowed through them. The words of Rev. Rev. 3:14-15+ must have hit home powerfully in Laodicea: the writer said that the church was as useless and distasteful as that bad water.4
The hot are the truly saved believers. The cold are those who are not believers and do not claim to be believers. The lukewarm are those who do claim to believe in Jesus, but are not truly regenerate believers.7
How shall we then understand this exclamation of the Saviour, . . . namely, by regarding the cold here as one hitherto untouched by the powers of grace. There is always hope of such an one, that, when he does come under those powers, he may become a zealous and earnest Christian. He is not one on whom the grand experiment of the Gospel has been tried and has failed. But the lukewarm is one who has tasted of the good gift and of the powers of the world to come, who has been a subject of Divine grace, but in whom that grace has failed to kindle more than the feeblest spark. The publicans and harlots were cold, the Apostles hot. The Scribes and Pharisees, . . . were lukewarm.8
2 Frederick William Danker and Walter Bauer, A Greek-English Lexicon of the New Testament and Other Early Christian Literature (Chicago, IL: University of Chicago Press, 2000), 337.
3 Colin J. Hemer, The Letters to the Seven Churches of Asia in Their Local Setting (Grand Rapids, MI: William B. Eerdmans Publishing Company, 1989), 188.
8 Richard Chenevix Trench, Commentary on the Epistles to the Seven Churches in Asia (Eugene, OR: Wipf and Stock Publishers, 1861), 195-196.