Revelation 3:15 – 16 says, "I know your works, that you are neither cold nor hot: I would you were cold or hot. So then because you are lukewarm, and neither cold nor hot, I will spew (vomit) you out of my mouth."
These verses have been interpreted to refer to the condition of the heart. You have never heard these verses interpreted correctly, if that is the only interpretation that you have heard.
It has often been said from the pulpit that God wants us to be red–hot for Him, and that He would even prefer us to be cold rather than lukewarm because then He could at least do something with us. The inference is that people with lukewarm hearts are impossible for God to work with. That statement reflects a lot of posturing from a pastor who is overconfident that he knows how to correctly interpret Scripture. It isn't true. Lukewarm Christianity is a disappointment to God, but God can help lukewarm Christians become red–hot for Him.
Nor does it stand to reason that God would prefer people to be cold and indifferent towards Him or dead set against Him, rather than in the process of warming up to Him. Matthew 24:12 says that in the last days, because iniquity shall abound, the love of many shall wax cold. Can anyone reasonably deduce from this verse that God is pleased with that kind of heart condition?
God is displeased with unrepentant sinners, so it is not logical to suppose that God prefers unrepentant sinners and backsliders to believers who live relatively decent lives, do little harm to others, and sometimes contribute much–needed good, but ought to cast off their self–righteousness and conceit and be passionate for Him in consideration of His position, His character, His deeds, and what He has done for us personally.
Revelation 3:15 – 16 really refers to delivering God's messages. The verses use drinks as an analogy. On a cold day, hot beverages and hot soups are big favourites. In hot weather, chilled water and juices are in great demand. Proverbs 25:13 says, "As the cold of snow in the time of harvest, so is a faithful messenger to them that send him: for he refreshes the soul of his masters." Conversely, the next verse indicates that there is no refreshing when someone fakes the anointing, "Whoso boasts himself of a false gift is like clouds and wind without rain."
In a charismatic church I attended, a pastor instructed those who were seeking to prophesy to not prophesy beyond the anointing. This is excellent advice. If God gives only a sentence and then the anointing lifts, stop right there. It is more to His glory if the Spirit directs another person in the assembly to pick up the thread and speak forth another short portion, then hands it over to yet another until the whole message is complete.
It is to a person's shame if they try to make themselves look more skillful in that gifting by adding their own words to extend the message. If we "beef up" the message, it amounts to despising the word that God gave us, deeming it to be inadequate. When someone prophesies beyond the anointing, the message falls flat. The good part becomes obscured. Some who sense that they are to prophesy might be prevented because the other person did not shut up and give them a chance to speak.
God might give a message, whether it is a word of prophecy or a sermon, that we feel the listeners are too immature to receive, and so it gets watered down to make it more palatable. This might take the form of the message being shortened, or couched in flattering words in the interest of "diplomacy" and "tact." Tact and diplomacy are beautiful – except for when plain speaking is called for, as in the case of Habakkuk 2:2. Though it was harsh, for the strengthening of His servants, the Lord wanted the prophet to make it very clear what He had to say.
Other Scriptural support can be found in Jeremiah 20:8 – 9 where Jeremiah complained that when he spoke the word of the Lord, he was persecuted because people didn't like it, so he kept his mouth shut, but then the word burned like a fire in his bones until he couldn't keep silent any longer. This is a good illustration of how it is necessary to say exactly what God has directed, even if it scorches the hearers and they consider the prophet or preacher to be a fanatic. If our hearts are tender towards the Lord, like they should be, our conscience and our love of truth won't let us alone if we don't say all that we are supposed to say when we are supposed to say it.
Who are we anyway, to decide whether people can receive what God instructs us to say, if He has given us a word to speak? God is the only one who really knows what is in people's hearts. Ezekiel 2:7 says, "And you shall speak my words unto them, whether they will hear, or whether they will forbear."
Of course, there is a place to be quiet, for the Bible tells us to not cast our pearls before swine, and Jesus withheld some things from His disciples because they were not able to bear them, but when God prods us to speak, it is our duty to speak, and let the chips fall where they may. It is in His hands whether our words will help to save souls, or stand as a testimony against them on Judgment Day.
Your word have I hid in my heart, that I might not sin against you.