“To the angel of the church of the Laodiceans write:
“The Amen, the Faithful and True Witness, the Beginning of the creation of God, says these things: I know your works, that you are neither cold nor hot. I wish you were cold or hot. So then, because you are lukewarm, and neither cold nor hot, I will spit you out of My mouth. For you say, ‘I am rich, and have stored up goods, and have need of nothing,’ yet do not realize that you are wretched, miserable, poor, blind, and naked. I counsel you to buy from Me gold refined by fire, that you may be rich, and white garments, that you may be dressed, that the shame of your nakedness may not appear, and anoint your eyes with eye salve, that you may see.

Revelation 3:14–18 — Modern English Version (Thinline Edition.; Lake Mary, FL: Passio, 2014)

The message here (so far) is to a church, a corporate-whole body of believers. Jesus is addressing the body as a whole. In so doing, this body gets a wretched report card. He calls them lukewarm.
To hear someone call any individual believer lukewarm is an immediate indication of abuse of this scriptural text. Oftentimes it is done to shame and/or control other Christians. Nevertheless… It is abuse.

So what now?

You find yourself in a congregation that appears very much like it is lukewarm (or maybe even cold.) Jesus is standing on the outside of this body, waiting to be let in. You don’t have to leave to have fellowship with Jesus. Perhaps the spark needed for a body to catch fire is yours.

There’s good news for you here.

Those whom I love, I rebuke and discipline. Therefore be zealous and repent. Listen! I stand at the door and knock. If anyone hears My voice and opens the door, I will come in and dine with him, and he with Me.

Revelation 3:19–20 — Modern English Version (Thinline Edition.; Lake Mary, FL: Passio, 2014)

If you’re a saved believer, that is you believe Jesus is the God-Man come to ransom you, forgive you of your sins, and give you eternal life. Jesus rebukes and disciplines. He never throws us out. We can repent of sins and have fellowship with Jesus restored.
If you’re not a saved believer, the invitation is to you, too.
Jesus stands at the door and knocks. Repentance is available to anyone, anytime in this life. If anyone individual hears His voice and opens the door… That is you believe He is. He died and rose again, ascended to heaven. And you’ve confessed your sin… You’ve opened the door.
He promises to fellowship with you.
To open the door to Jesus, it’s easy.

Acknowledge that you are a sinner and completely unable to get to heaven on your own merit. And that Jesus is Who He claimed to be, God.

Believe that Jesus died on the cross for your sins, and rose again to give you eternal life.

Confess those facts aloud, with your mouth. Confess your sins, ask for forgiveness and receive the gift of eternal life.