Question:
Revelation 3:16: “So then because thou art lukewarm, and neither cold nor hot, I will spue thee out of my mouth.”

Does being lukewarm have to do with salvation?

Answer:
Lukewarm is a condition of a person being neither “cold” nor “hot” for the Lord. This condition makes it hard to discern who is a Christian and who is not a Christian.

When the Lord takes the believers home at the rapture of the church 1 Thessalonians 4:15-18, there will be a mass of people that will be left behind because they are mere professors.
In John 14:23: “Jesus answered and said unto him, If a man love me, he will keep my words: and my Father will love him, and we will come unto him, and make our abode with him.
Spewing out of the mouth is not in reference to true believers, but to mere professors.