In his homily on Tuesday, Pope Francis spoke of how we must never be content with where we are in the spiritual life, but rather must seek constant conversion.

The Pope addressed those present in the Vatican's Saint Martha guesthouse for his Nov. 18 daily Mass, saying that the Lord constantly calls us to conversion, and condemned "those who live by appearances, Christians of appearances."

"Appearances are these Christians' shroud: they are dead….Am I one of these Christians of appearances? Am I alive inside, do I have a spiritual life? Do I hear the Holy Spirit, do I listen to the Holy Spirit, do I move forward?" he asked.

The pontiff centered his reflections on the day's readings, the first coming from the Book of Revelation, and the Gospel from the 19th chapter of Luke, in which the tax collector Zacchaeus climbs a tree in order to see Jesus, who then asks to dine at the corrupt man's house.

As the Church is coming to the close of its liturgical year we are always invited to think about conversion, he said, explaining that the day's first reading offers an image of what the Lord says to those who have become lukewarm and comfortable in their faith.

These are the people who think: "I do what I can, but I am at peace and do not want to be disturbed…I go to Mass on Sundays, I pray a few times, I feel good, I am in God's grace, I'm rich (and) I don't need to do anything."

Pope Francis warned that this state of mind is sinful, and that "feeling spiritually comfortable is a state of sin" which the Lord strongly condemns when he says that he will spit the lukewarm out of his mouth.

The Lord also calls to conversion to those "who live by appearances," the Roman Pontiff observed, explaining that these are the Christians who believe that they alive and living a good life, but are really dead.

These type of Christians are called to convert, because "if everything looks good, I have nothing to reproach myself about: I have a good family, people do not gossip about me, I have everything I need…Appearances! Christians of appearance...they are dead!"

Rather than believing that we are already doing enough because we are in the grace of God, we must search for "something alive" within ourselves and constantly seek to reawaken it so that we can advance "from appearances to reality" on our path of conversion, the Pope continued.

He then spoke of the tax collector Zacchaeus from the Gospel, noting how "he was just like many leaders we know: corrupt. Those who, instead of serving the people, exploit the people to serve themselves."

Despite his corrupt heart, Zacchaeus was not lukewarm, but rather in a state of "putrefaction," the pontiff said, and he was able to feel something inside drawing him to Jesus.

What Zacchaeus felt, the Pope explained, was curiosity in the face of a man who he had heard so much about. So the Holy Spirit "sowed the seed of curiosity, and in order to see (Jesus) this man even does something a little 'ridiculous'" by climbing a tree.

Because the Holy Spirit was working inside of him Zacchaeus wasn't ashamed to be seen in the tree, despite being an important leader in society, the Bishop of Rome noted, and because of this, he was able to experience the joy of meeting Christ.

"Those of comfort and those of appearance had forgotten what joy was (but) this corrupt man immediately gets it" and promises to give back everything he has stolen and more, the Pope observed, adding: "When conversion touches pockets, it's a certainty."

Pope Francis concluded his homily by recalling the three calls to conversion that Jesus himself makes to the comfortable, the lukewarm and those who live under appearances, thinking they are rich, when they are actually poor.

He encouraged those present to use the final weeks of the liturgical year to be vigilant and think "very, very seriously about our conversion, so that we can move forward on the path of our Christian life."