What is a lukewarm Christian?

"Lukewarm Christians will be punished, some more and some less. Get busy and active in the will of God."
You said this yet did not add scripture since its not written. Lets speak truth not lies.

Luke 12 who was a Christian there? Christ had not rose so there were none. He said it best lets leave it there.
"Those whom I [dearly and tenderly] love, I rebuke and discipline [showing them their faults and instructing them]; so be enthusiastic and repent [change your inner self—your old way of thinking, your sinful behavior—seek God’s will]."

See Rev 3:20 comes later. He shines His love. We always seem to look at others not self. LukeWarm Christians are loved forgiven shown mercy grace and compassion. Christ already died for the sin of the world. He already took the punishment. yet you say those that were bought with a price and have fallen...watch out your going to get punished. Fear not of God

Lukewarm is part of the pattern of revelation speaking of mixing. Don't mix seed, cloth, yoked animals, calf and mother's milk, etc. This pattern addresses the issue of not properly identifying the nature of God as both Holy and Love. We are not to use philosophy to explain God, but the cross.

The primary dualism of scripture is not good/evil or flesh/spirit. It is in the revelation of God about himself. He is Holy and Love.
If we try to understand these things we get confused. If we see a prisoner go free, we do not marvel at the wonderful grace, but complain there is no justice. If we are the prisoner and are not let free, we do not praise the wonderful justice, but complain there is no mercy.

God revealed himself as Holy through the law, and love through the substitutionary sacrifices. He brought the two 'words' together on the cross.

Say Shibboleth one way you die, one way you live. If you speak it as a single corn...which must die, you die. If you speak of it as a full ear, as in the fruit of the resurrection, then you live.

The lukewarm Christian is the one who does not properly preach the cross and thereby make the Father known, but has a cartoon religion of his own making taking elements of Holiness and Love and mixing them poorly.