This Gospel passage is short and packed with meaning, alluding to the Old Testament and other Jewish writing. It can cause some cognitive dissonance with the culturally peaceful non-judgemental Jesus. Or that this is just a form of rabbinical hyperbole to make a point. There is undoubtedly an aspect of that when it seems Jesus is saying that his mission is to bring division.
The first two lines involve casting fire and a baptism that Jesus is to receive. We have the imagery of fire and water. As Brant Pitre refers, this is “a pretty standard Jewish theme in apocalyptic Jewish writings (prophetic writings)” along with outside the Bible. That the earth was destroyed the first time through water and later destroyed through fire, this destruction by fire is also a New Testament theme such as in 2 Peter 3, saying “the heavens and the earth will be dissolved with fire”.
Returning to Brant Pitre:
So this image of water and fire, of destruction by flood and then destruction by fire, is not just standard Jewish eschatology, it’s also the teaching of the New Testament. It’s standard Christian Eschatology that in the Second Coming the world will be cleansed by fire and not by flood.
Jesus uses baptism as referring to his crucifixion and death in other places, such as when James and John request that they will be placed on his left and right side when he comes into glory. Jesus replies, ‘You do not know what you are asking. Are you able to drink the cup that I drink or be baptized with the baptism with which I am baptized?’ There is a connective thread between baptism and fire when John the Baptist predicts, “he will baptize you with the Holy Spirit and with fire.” Both are used for cleansing and purification.
Paragraph 696 of the Catechism says:
While water signifies birth and the fruitfulness of life given in the Holy Spirit, fire symbolizes the transforming energy of the Holy Spirit’s actions. The prayer of the prophet Elijah, who “arose like fire” and whose “word burned like a torch,” brought down fire from heaven on the sacrifice on Mount Carmel. This event was a “figure” of the fire of the Holy Spirit, who transforms what he touches. John the Baptist, who goes “before [the Lord] in the spirit and power of Elijah,” proclaims Christ as the one who “will baptize you with the Holy Spirit and with fire.” Jesus will say of the Spirit: “I came to cast fire upon the earth; and would that it were already kindled!” In the form of tongues “as of fire,” the Holy Spirit rests on the disciples on the morning of Pentecost and fills them with himself. The spiritual tradition has retained this symbolism of fire as one of the most expressive images of the Holy Spirit’s actions. “Do not quench the Spirit.”
Chapter 12 of Luke goes into the details of what discipleship means. That there will be persecution, and you will be accountable and must remain vigilant. In this passage, Jesus warns that discipleship is not a cakewalk. That following him will mean that there will be division among family members. “Salvation history is full of familial conflict that has its origins in differing relationships to God.”
As John Bergsma notes:
Jesus’s primary mission was not to establish social peace in this world and in this life. If that had been his mission—and many think it was!—he obviously has failed. Instead, Jesus’s mission was to reveal, to those who desire it, the “narrow gate” that leads to salvation (Matt 7:13–14, RSV2CE), the Way that is himself (John 14:6). There is a price too high to pay for peace. And that price is infidelity to Christ. 
What Jesus is saying can be seen as a reference to Micah 7:6–7:
for the son treats the father with contempt, the daughter rises up against her mother, the daughter-in-law against her mother-in-law; a man’s enemies are the men of his own house. But as for me, I will look to the Lord, I will wait for the God of my salvation; my God will hear me.
Peter Kreeft describes this concretely:
Jesus came to bring peace with God, not the devil; with ourselves, our true selves, not our foolish flesh; and with our neighbors, not with the world order that so often pits us against our neighbors. Jesus came to make war against the devil because the devil is at war with God. Jesus came to make war against the flesh because the flesh is at war with the Spirit, the Holy Spirit (not with the soul; the soul is part of the flesh). And Jesus came to make war against the world because the world is at war with the Church, which is the communion of saints. So much so that in every culture saints are martyred, whether in red or in black and white, whether in blood or in print.
Elsewhere Jesus tells us to pick up the cross daily. He never downplays the cost of discipleship. Following Christ can mean that our self-inflicted wounds can be healed, where we are suffering because of our sins. To love others is to enter into suffering. This suffering-love is why the Father sent Jesus and the Holy Spirit to us.
Jesus is telling us that our problems will not go away and that there will be dissension even within our own families.
In John 16:33 Jesus says:
I have said these things to you, that in me you may have peace. In the world you will have tribulation. But take heart; I have overcome the world.”
I know I was somewhat naive on my journey and conversion to Christ. I believed a host of problems would disappear, but instead, some of the most challenging parts of my life immediately followed.
As Brant Pitre puts it:
“There’s not going to be any salvation without tribulation first. There’s not going to be any kingdom of peace without a time of division first. I have to cast a fire of judgment upon the world and go through the waters of the cross before we can reach the resurrection.” Does that make sense? There’s no resurrection without a cross. There’s no kingdom without tribulation. There’s no restoration without division. He’s correcting an overly optimistic eschatology, or expectation that his disciple might be thinking.
- Peter Kreeft, Food for the Soul: Reflections on the Mass Readings Year C
- The Word of the Lord: Reflections on the Sunday Mass Readings for Year C – John Bergsma
- Catholic Productions, Commentaries by Brant Pitre
- Catechism of the Catholic Church, 2nd Edition
- Photo by Ben White on Unsplash
- Catholic Productions, Brant Pitre ↩
- Catholic Church. (2000). Catechism of the Catholic Church (2nd Ed). United States Catholic Conference. ↩
- The Word of the Lord: Reflections on the Sunday Mass Readings for Year C, John Bergsma ↩
- Peter Kreeft, Food for the Soul: Reflections on the Mass Readings Year C ↩