Lukewarmness refers to those who are only christian in name only, they may go to mass every week, say they are christian people, but the beliefs and faith is not a big part of their life in the real world, they basically ‘put in’ their one hour per week, and thats where it ends.
I like the term ‘fair weather christians’, those that claim to be christian ONLY when its good or beneficial in some way for them, when times get tough or its not too popular to be in that group, they will deny it.
A good example would be a killer going around asking people if they are christian or not, and killing those who answer yes, Jesus warned us such things would eventually happen, many would be arrested, tortured, imprisoned due to his name, but when a ‘lukewarm’ person is asked this question under threat of death, they would answer no or refuse to answer (basically the same thing as a no)…yet they do not realize how huge this is, they have denied God, no coming back from that imo.
I think the bible actually mentions entire churches that are lukewarm, by looking around in modern times, its fairly easy to spot ‘lukewarm’ churches