"Do we have an attitude of spiritual tepidness, transforming our lives into a cemetery where there is not life? If so, God calls us to conversion and we say yes but tomorrow." (Pope Francis)

I like his analogy of the cemetery. Spiritual tepidness is another way of saying spiritual lukewarmness. Some spiritual writers see this to be a silent killer of one's spiritual life. They liken it to what high blood pressure is to the human life, a silent killer. Untreated it can be too late.

The Book of Revelation addresses this spiritual lukewarmness in Chapter 3. “To the angel of the church in Laodicea write this: ‘The Amen, the faithful and true witness, the source of God’s creation, says this:'I know your works; I know that you are neither cold nor hot. I wish you were either cold or hot. So, because you are lukewarm, neither hot nor cold, I will spit you out of my mouth.'" (Rev 3:14-16)

What does lukewarmness look like? Our heart is not in growing in holiness. We go through the motions but our focus is elsewhere. We are comfortable doing the bare minimum. There is a sense of spiritual laziness. 

The Catechism of the Catholic Church describes lukewarmness in these words. It is a "hesitation of negligence in responding to divine love," adding that it "can imply refusal to give oneself over to the prompting of charity" (2094).