In the Hebrew Scripture fire symbolizes the word of God pronounced by the prophet. But it also signifies the divine judgment that purifies his people by passing in their midst.
We can say the same about the word of Jesus: it builds up, but at the same time it destroys everything that has no consistency, everything that needs to come down, everything that is vanity, and it leaves only the truth standing.
John the Baptist had said of him: “He will baptize you with the Holy Spirit and fire” (Lk 3:16), preannouncing the Christian baptism inaugurated on the day of Pentecost with the outpouring of the Holy Spirit and the appearance of the tongues of fire (See Acts 2:3).
This then is Jesus’ mission: to cast fire on earth, to bring the Holy Spirit with his renewing and purifying force.