Poole on Revelation 3:15, 16: Nauseating Lukewarmness
Verse 15: (Rev. 3:1) I know thy works, that thou art neither cold nor hot: I would thou wert cold or hot.
[I know thy works] He describes that sort of man that visits the assembly of Christians, and joins himself to them, but does not establish his life according to the pattern of the Gospel: such also Paul describes in 2 Timothy 3:5, 7. See also Matthew 7:22 and Hebrews 10:29. Not far hence was that one departing unto whom Epictetus in Arrianus’ Discourses of Epictetus 4:7 said, ἐπιπέπηγας ἤδη τὸ ἐν τῇ ῥιζῃ κάτω, τὰ δὲ ἄνω οὐ μακρὸν ἔτι ἀνθεῖ, thou hast already frozen the thing in the root downwards, so it will send upwards those things not much longer (Grotius).
[That, etc., ὅτι οὔτε ψυχρὸς εἶ οὔτε ζεστός] Quia/that (or, that is, quòd/that [Pagnine, thus Beza, Piscator]) thou art neither cold nor hot (Erasmus, Pagnine, etc.). Cold are, either, 1. infidels (Ambrose and Gregory and a great many in Ribera), that openly declare hatred for Christ, like the Jews, Pagans, etc., in whom love grows completely cold, Matthew 24:12 (Cluverus); who have no acquaintance with the Gospel (Grotius, similarly certain interpreters in Estius, Durham, Pareus), and hence not any Christian affections (Grotius); who are free from every form and profession of religion (Durham). To which the following wish is a hindrance, for the condition of the Christian sinner is undoubtedly better, and closer to salvation, than of the infidel. Or, 2. Christian men full of sins (Ribera), clearly destitute of the grace and illumination of the Holy Spirit (Gagnæus); obviously and flagrantly evil (Tirinus, Estius), bound by many and great sins (Ribera). Hot are the truly (or fervently) good (Estius, similarly Tirinus), who are fervent in spirit, according to Romans 12:11 (Gagnæus), either, in faith (Ribera out of Ambrose), or, in love (Ribera, similarly a great many in Zegers); who were endowed with Christian love, which is compared to Fire, as is all love. See Song of Songs 8:7 and the things said there (Grotius); who with a profession have also force, fervor, life, and renewal (Durham); who are ablaze with the love of God and neighbor (Pareus).
I know thy works; I know and observe thy behaviour, thy ministerial function. That thou art neither cold nor hot; thou art neither openly profane and grossly scandalous, like heathens, or such as make no profession; nor yet hast thou any true zeal or warmth, either for the faith once delivered to the saints, or in love to God, seen in keeping his commandments, having the power and efficacy of godliness, teaching thee to deny all ungodliness and worldly lusts, Titus 2:12. Thou hast a form of godliness, but deniest the life and power thereof.
[I would (ὄφελον, אַחְלָי, would that: Dioscorides, Galen, and others make use of it [Grotius]) thou wert cold or hot] He does not intend this absolutely, but comparatively (Pareus, similarly Gomar); not that this is desirable, but that it is more to be desired, that is, less to be detested, than to be tepid (Estius). It is not to be thought that Christ wishes or directs him to be cold, or to be indifferent with respect to cold and heat; but after the fashion of men He expresses His hatred and detestation of a hypocritical profession; for not all parts of a similitude are to be pressed or urged, as if from this it is evident that He sets cold and heat in the same place and values them equally (Durham). The sense: It is preferable, or it is less evil, to be cold (Gagnæus), that is, to be a complete stranger to the faith (certain interpreters in Zegers, similarly Pareus, Durham), than to be tepid (Gagnæus), or a hypocrite (Pareus); that is, than after having received the faith to act half-Christian (certain interpreters in Zegers). [Question: Why, or, how is that better?] Response 1: Because it is a lesser [sin] to be ignorant of the truth than not to make use of what is known (Grotius, similarly Pareus, Durham), Luke 12:48; 2 Peter 2:21, on which places see what has been said (Grotius). For beyond that he that is called tepid is in fact cold, and is without all religion, He also adds these two things: 1. that he feigns piety, and therefore tempts God, as in Acts 5:3, etc., as if He were not able to discern hypocrisy, or would approve it; 2. that such a one, although poor, is nevertheless arrogant and full of presumption, as in verse 17, which God especially hates (Durham). Hence feigned holiness is a twofold iniquity (Estius). Response 2: For the state of the tepid, who are held by some sins, even if that state be less evil than that of the cold, who commit much graver sins, is yet much more dangerous (Ribera). There is greater hope of the conversion of the cold than of those that have an appearance of holiness (Estius, similarly Durham). There is a greater hope of health ἐν ἀκολάστῳ, in the intemperate, than ἐν ἀκρατεῖ, in the incontinent, as Aristotle shows (Grotius). See Matthew 21:31, 32 (Durham). The cold is more readily converted than the tepid, since he sees his danger as apparent, and his damnation as certain, which the tepid does not fear, nor see; and therefore he does not think of a change of life, nor seek a physician (Ribera). Response 3: For a profession of religion without its virtue pollutes the name of God, and exposes it to ignominy. See Ezekiel 20:39 (Durham). The sense: Would that thou wert good, or openly evil, and full of perturbations, so that thou mightest recover thyself from those untroubled (Drusius’ Classes of Proverbs 1:3:41 out of Vallessius). He by no means desires that he be cold, that is, impious or infidel; but that he might acknowledge himself to be cold, whereby he might thus come to spiritual ardor (Zegers).
I would thou wert cold or hot: we must not think Christ wisheth any persons cold absolutely, but comparatively, intimating to us, that the condition of a downright atheist, or profane person, is more hopeful than that of a close, formal hypocrite: the latter is in the road to hell as well as the other, and no more pleaseth God than the other. It is better not to have known the truth, than knowing it, to live contrary to it, Luke 12:48; 2 Peter 2:21. Commonly such men also are proud, and self-conceited, having something to stop the mouth of their natural conscience, harder to be convinced of their evil state, Matthew 21:31, 32.
Verse 16: So then because thou art lukewarm, and neither cold nor hot, I will spue thee out of my mouth.
[But, etc., οὕτως ὅτι χλιαρὸς εἶ] Οὕτως/thus/so here is not of similitude (Schmidt), but syllogistic (Schmidt, similarly Glassius’ “Grammar” 3:5:29:510), and it means עַל־כֵּן, upon thus, therefore. In the Glossary, χλιαρὸν/tepid. Aristotle, Galen, and others use it (Grotius). Thus (or, and so [Erasmus, Beza, Piscator, etc.]) because thou art tepid (Montanus, Erasmus, etc.). He is here called tepid that fluctuates between virtues and vices (Lapide out of Haymo and Anselm and Lyra, Drusius’ Classes of Proverbs 1:3:41 out of Jerome), whom Hermas, in Shepherd of Hermas 3:8, calls dubium/wavering (Grotius); who serves equally God and Mammon, Matthew 6:24. Compare 1 Kings 18:21 (Cluverus), partly and secretly evil, partly and apparently good (Tirinus); who desires to live according to virtue, but flees the contest with vices and the labor of virtue (Lapide out of Anselm, etc.); who does not dare knowingly and willingly to offend God gravely, yet neglects the study of a purer and more perfect life, whence he surrenders himself to his lusts, etc. (Menochius); who has a certain loose and imperfect virtue (certain interpreters in Drusius’ Classes of Proverbs 1:3:41): who under the appearance of a good man is iniquitous and impenitent (Drusius out of Vallessius); who, although he be not actually good, thoroughly persuades himself that he is good, and therefore swells with pride, and is pleasing to, and trusts in, himself, and lives securely, as if needing nothing and fearing nothing, of which sort were the Pharisees, etc. (Pererius). By tepid here He understands a lazy negligence in duty (Gomar), and a manifest abating of zeal for the glory of God, and of piety (Gomar, similarly Durham, Piscator on verse 15); and that this Church rested in this, that it had fled from Idolatry and profanity and corrupt doctrines, but was at the same time devoid of zeal, as it is indicated in verse 19 (Durham).
[Neither cold nor hot] He explains more clearly what χλιαρός/tepid is (Grotius). Not completely devoted to piety, not entirely ἄθεος/atheistical (Drusius’ Classes of Proverbs 1:3:41).
Neither cold nor hot; partly good, partly bad, having something of profession, nothing of the life and power of religion; contenting thyself that thou art not a Jew, nor a pagan; not a superstitious, idolatrous person; but a Christian, a protestant, a minister, or member of the Reformed church; yet neglecting thy duty both as a minister, and as a Christian, living in a sensual satisfaction of thy lusts.
[I will begin, etc., μέλλω σε ἐμέσαι, etc.] It is about to be that I will vomit thee, etc. (Beza, Piscator, Pagnine, etc.), that is, I will cast away or destroy (Piscator): the vail of hypocrisy I will remove from thee; thy turpitude to all I will reveal; thy reputation, which thou seekest by this outward profession, I will turn into contempt and hatred of thee, and I will show by thy punishment how I hate thee (Durham). He continues the analogy (Grotius). Tepid things are ἐμετικὰ, or provoke vomiting (Grotius, thus Ribera, Menochius, Cotterius). Celsus’ The True Word 1:2, He who wishes to vomit after food, if he would do it with ease, ought previously to imbibe tepid water. Now, Christ signifies that such men are troublesome to themselves, like those things which cause nausea. Christ vomits out those that He ceases to admonish. A similar figurative expression, when someone is said not to be able to digest a certain thing (Grotius).
I will spue thee out of my mouth; I will cast thee off, as men vomit up lukewarm things.
 Greek: Οἶδά σου τὰ ἔργα, ὅτι οὔτε ψυχρὸς εἶ οὔτε ζεστός· ὄφελον ψυχρὸς εἴης ἢ ζεστός.  Lucius Flavius Arrianus of Nicomedia was a second century Greek historian and a Roman senator. He was a pupil of the Stoic philosopher, Epictetus (c. 50-135).  Anabasis.  Gregory the Great (c. 550-604) was elected Pope in 590. He was a monk, scholar, prolific author, and, having been made pope, instrumental in reinvigorating the missionary work of the Church.  Padanius Dioscorides (c. 40-c. 90 AD) was a Greek physician and pharmacologist. He traveled all over the Roman world in search of substances with medicinal properties. He wrote a five volume work, De Materia Medica, which was in use until the seventeenth century.  Nicomachean Ethics 1.  See Matthew 9:12.  Francis Vallessius, or Vallès, was a Spaniard, and served as physician to Philip II.  Greek: οὕτως ὅτι χλιαρὸς εἶ, καὶ οὔτε ψυχρὸς οὔτε ζεστός, μέλλω σε ἐμέσαι ἐκ τοῦ στόματός μου.  Celsus was a second century Greek philosopher and opponent of Christianity. Excerpts from his The True Word are found in Origen’s Contra Celsum.