Rev 3:15-16 "I know your works, that you are neither cold nor hot. I could wish you were cold or hot. "So then, because you are lukewarm, and neither cold nor hot, I will vomit you out of My mouth.”

The use of hot and cold streams that were present in Laodicea was applied to a spiritual illustration for the church.  As hot and cold were used also for medicinal purposes, once they are combined they were useless. Jesus is speaking to a church, of their works having no value, they are not done in Christ (Eph.2:10). The Lord was disgusted with them saying they were his and not do any works exhibiting him working among them.

We find these terms rarely used in this way. Certainly it refer to the latter times when Jesus said

And because lawlessness will abound, the love of many will grow cold.” (Mt 24:120). Our love is exhibited by actions, our works (James addresses this as showing ones true faith).

This particular church is described in Rev. 3:17-18 As them saying 'I am rich, have become wealthy, and have need of nothing' they had no trials, everything was going smoothly.

Jesus responded by saying they are unaware they are “wretched, miserable, poor, blind, and naked” If they were hot or cold he could chasten them and move them to the place he wants them to be. V.18 "I counsel you to buy from Me gold refined in the fire, that you may be rich; and white garments, that you may be clothed, that the shame of your nakedness may not be revealed; and anoint your eyes with eye salve, that you may see.”

But instead they have not allowed him to work among them, this is why He says to individuals, "Behold, I stand at the door and knock. If anyone hears My voice and opens the door, I will come in to him and dine with him, and he with Me” (Rev. 3:20)