"Lukewarm" does NOT mean backslidden Christians! If you're a backslidden Christian, you STILL have the Holy Spirit within you. HE is what makes you "hot", not the measure of your walk with the Lord.
HOT = Christian
COLD = Athiest
LUKEWARM = Undecided (unsaved)
Only those who are "hot" with the light of life (Holy Spirit) will be in Heaven. Those who are undecided will be rejected, even if they thought they were in good with God, because they are not indwelt with the Holy Spirit. These are likely the "good people" who never accepted Christ.
Again, a backslidden Christian is STILL a Christian! They are STILL hot, because it is not the quality of our walk that makes us "hot", but Yeshua Himself, Amen? Likewise it is not our works that saves us but Yeshua alone. We have no righteousness apart from the righteousness in Yeshua.
Therefore, our God is a consuming flame, He baptises us with fire, and it is His Shekinah Glory that makes one "hot" before His Throne. We have no holiness, no righteousness, no...heat apart from Him.
God does not use this hot/cold reference like a child would on the playground, but rather, whether or not you have the Life of the Most High burning inside of you. Even backsliders have this Life if we are to believe it is by grace through faith we are saved and not by works lest anyone should boast.
The father NEVER disowned his prodigal son, even if the son thought he had. When he returned home with his tail between his legs, thinking it was better to be a servant than nothing at all, the father welcomed him with a feast and rejoicing. Despite his carousing, he had kept his esteemed position as son in the house of his father.
Whom have I in heaven but You? And there is nothing on earth that I desire besides You. My flesh and my heart may fail, but God is the strength of my heart and my portion forever. ~~Psalm 73:25-26 (ESV)