There is a whole book on the subject, and it is excellent! The following excerpts are from *Lukewarmness: The Devil in Disguise *by Francis Carvajal (Scepter Publishers). I suggest you find the book if you want to read more.
Lukewarmness may be understood as a general breakdown of the theological virtues … Christians fall ino lukewarmness because of culpable neglect … Everything having to do with the supernatural is reduced to “doing things” rather than “loving Someone” …
Lukewarmness involves a wholehearted disdain for prayer and sacrifice, a preoccupation with selfish concerns and comfort, a complete lack of refinement in dealings with God, a coarse and slothful approach to anything which pertains to the Lord … [citing P. Rodriguez]
Lukewarmness is a grave sickness of soul which can strike at any stage of one’s interior life. We say that a tepid soul has “fallen away.” It has grown weary of the interior struggle …
St. Thomas defines lukewarmness as “a kind of sadness which makes a person sluggish in the performance of spiritual exercises on account of the effort they require” …
Lukewarmness means “softness, laziness bent on the easiest, most pleasurable way, any apparent shortcut, even at the expense of infidelity to God.” [citing Josemaria Escriva] …
So, yes, a person who goes to Sunday Mass but is not into the faith could most definitely be called lukewarm. I’ve been there, done that, thrown away the t-shirt.
