From: Luke 12:49-53
Jesus the Cause of Dissension
(Jesus said to His disciples,)  "I came to cast fire upon the earth; and would that it were already kindled!  I have a baptism to be baptized with; and how I am constrained until it is accomplished!  Do you think that I have come to give peace on earth? No, I tell you, but rather division;  for henceforth in one house there will be five divided, three against two and two against three;  they will be divided, father against son and son against father, mother against daughter and daughter against her mother, mother-in-law against daughter-in-law and daughter-in-law against her mother-in-law."
49-50. In the Bible, fire is often used to describe God's burning love for men. This divine love finds its highest __expression in the Son of God become man: "God so loved the world that He gave His only Son" (John 3:16). Jesus voluntarily gave up His life out of love for us, and "greater love has no man than this, that a man lays down his life for his friends" (John 15:13).
In these words reported by St. Luke, Jesus Christ reveals His abounding desire to give His life for love of us. He calls His death a baptism, because from it He will arise victorious never to die again. Our Baptism is a submersion in Christ's death, in which we die to sin and are reborn to the new life of grace: "We were buried therefore with Him by baptism into death, so that as Christ was raised from the dead by the glory of the Father, we too might walk in newness of life" (Romans 6:4).
Through this new life, we Christians should become set on fire in the same way as Jesus set His disciples on fire: "With the amazing naturalness of the things of God, the contemplative soul is filled with apostolic zeal. `My heart became hot within me, a fire blazed forth from my thoughts' (Psalm 38:4). What could this fire be if not the fire that Christ talks about: `I came to cast fire upon the earth, and would that it were already kindled' (Luke 12:49). An apostolic fire that acquires its strength in prayer: there is no better way than this to carry on, throughout the whole world, the battle of peace to which every Christian is called to fill up what is lacking in the sufferings of Christ (cf. Colossians 1:24)" ([St] J. Escriva, "Christ Is Passing By", 120).
51-53. God has come into the world with a message of peace (cf. Luke 2:14) and reconciliation (cf. Romans 5:11). By resisting, through sin, the redeeming work of Christ, we become His opponents. Injustice and error lead to division and war. "Insofar as men are sinners, the threat of war hangs over them and will so continue until the coming of Christ; but insofar as they can vanquish sin by coming together in charity, violence itself will be vanquished" (Vatican II, "Gaudium Et Spes", 78).
During His own life on earth, Christ was a sign of contradiction (cf. Luke 2:34). Our Lord is forewarning His disciples about the contention and division which will accompany the spread of the Gospel (cf. Luke 6:20-23; Matthew 10:24).
Source: "The Navarre Bible: Text and Commentaries". Biblical text taken from the Revised Standard Version and New Vulgate. Commentaries made by members of the Faculty of Theology of the University of Navarre, Spain. Published by Four Courts Press, Kill Lane, Blackrock, Co. Dublin, Ireland. Reprinted with permission from Four Courts Press and Scepter Publishers, the U.S. publisher.