A.T. Robertson Commentary Revelation 3:15

"I know thy works, that thou art neither cold nor hot: I would thou wert cold or hot." — Revelation 3:15 (ASV)

Neither cold (ουτε ψυχρος). Old word from ψυχω, to grow cold (Matthew 24:12), in N.T. only Mt 10:42 and this passage.

Nor hot (ουτε ζεστος). Late verbal from ζεω, to boil, (Romans 12:11), boiling hot, here only in N.T.

I would thou wert (οφελον ης). Wish about the present with οφελον (really ωφελον, second aorist active indicative of οφειλω, without augment) with the imperfect ης (instead of the infinitive) as in 2 Corinthians 11:1, when the old Greek used ειθε or ε γαρ. See 1 Corinthians 4:8 for the aorist indicative and Ga 5:12 for the future.