Revelation 3:15-16
15 I know thy works, that thou art neither cold nor hot: I would thou wert cold or hot.
16 So then because thou art lukewarm, and neither cold nor hot, I will spue thee out of my mouth.
The Grace New Testament Commentary - Revelation 3:15-16
3:15-16 The Judge found nothing in this church to commend. Their works were not like cold water that refreshes, or like hot water that soothes and stimulates. They had no cool water for the spiritually thirsty people around them (cf. John 4:13-14), nor were they hot enough spiritually to stir up one another's faith. In reality, this church was like water that was lukewarm, not fit for anything. Because of this the Lord told them that He will "spew them out of His mouth," that is, punish them for their sin (cf. Lev 18:24-28).
The Evangelism Study Bible - Revelation 3:16-19
3:16-19 While true believers can never lose their relationship with the Lord (see John 5:24), indifference that causes us to be unproductive as Christians is distasteful to God and brings divine discipline (see Heb. 12:3-11).