The degrees [Hot, Cold, and Lukewarm] of water represents the condition of one’s heart.
Lukewarm comprises of both cold and hot water. When both degrees of water come together, both get affected in a negative way. The cold water does not make the other water cold nor does the hot water make the other as hot, but both get compromised and become less of what they were.
Lukewarm is the result of combining both hot and cold which is reconciling the truth with the lie.
When a professing believer in Christ becomes too much like the world, he becomes less like God. His light gets faint [resembling a lukewarm person].
The good news is that God brings us back before we become completely lukewarm [Hebrews 12:5-6].
Lukewarm is synonymous with apostasy. I will illustrate this with the hot water representing an individual who believes in the truth found in God’s Word and the cold water an unsaved person. When the person who is holding on to the truth [hot water] intakes and believes in some worldly philosophies [Evolution, Cultic doctrine, New Age, and etc.] and intermingles it with Biblical doctrine, they have compromised the truth of God’s Word and has become lukewarm in belief and lifestyle, in other words, they became a liberal Christian [believing in a different Jesus and accepting the world’s teachings] which is full-blown apostasy.
If you notice in Matthew 7:17-18, it says, “17 In the same way, every good tree produces good fruit, but a bad tree produces bad fruit. 18 A good tree can’t produce bad fruit; neither can a bad tree produce good fruit.”
The tree illustrates 2 types of people and if you notice, a third is not mentioned. Lukewarm does not mean that the person is half Christian, but it means the same as a bad tree. The reason is given in Revelation 3:16 which says, “So, because you are lukewarm, and neither hot nor cold, I am going to vomit you out of My mouth.”
The lukewarm who is a professing Christian is not really one as he is expunged by force/rejected by Jesus “vomit you out of My mouth.”
Jesus will never reject those who are truly His…John 6:37 “Everyone the Father gives Me will come to Me, and the one who comes to Me I will never cast out.”
A true lukewarm person is one that is not fully committed to Jesus and is devoid of the Holy Spirit.