Luke 12:49

I am come to send fire on the earth. By this fire, some understand the light of the gospel, and the fire of charity and divine love. Others, the fire of trials and persecutions. (Witham) --- What is the fire, which Christ comes to send upon the earth? Some understand it of the Holy Ghost, of the doctrine of the gospel, and the preaching of the apostles, which has filled the world with fervour and light, and which was signified by the flames of fire which appeared at the descent of the Holy Ghost upon the apostles. My words, says the Lord, in Jeremias, (Chap. xxiii. 29.) are as a fire, and as a hammer, that breaketh the rock in pieces. Others understand it of the fire of charity, which Christ came to enkindle upon the earth, and which the apostles carried throughout the whole world. But the most simple and literal opinion seems to be, the fire of persecution and war. Fire is often used in Scripture for war: and our Saviour declares in St. Matthew that he is come to bring the sword, and not peace; that is, the doctrine of the gospel shall cause divisions, and bring persecutions, and almost an infinity of other evils, upon those who shall embrace and maintain it. But it is by these means that heaven must be acquired, it is thus that Jesus Christ destroys the reign of Satan, and overturns idolatry, superstition, and error, in the world. So great a change could not be made without noise, tumult, fire, and war. (Calmet)