Do not think that I have come to bring peace upon earth. I have come to bring not peace but the sword. There has never been any contention that Jesus Christ is indeed the Prince of Peace to whom the prophet Isaiah alludes in his famous prophecy (cf. Isaiah 9:5-6). For as St. Paul reminds us, it is in Jesus Christ that the reconciliation, both between man and man as well as between man and God is attained (cf. Ephesians 2:11-22). Moreover, as Jesus was getting ready to take leave of his disciples, he bequeathed upon them peace as his departing gift to them (cf. John 14:27a). It was Christ’s peace that was to fill the void that his going away would create. But even as we rejoice in Christ’s gift of peace to us, we should be careful to always keep in mind his rejoinder that the peace he was bequeathing his disciples is not of this world (cf. John 14:27b). If we don’t, then the above words of Jesus which we hear in today’s Gospel Reading might come to us as a shocker. At any rate, Jesus was not saying anything new. The priest Simeon had already spoken those words during Jesus’ presentation in the temple (cf. Luke 2:33-34). What should we make, then, of Jesus’ words that he has come not to bring peace but rather to cause division? How can we reconcile the above words of his with the fact that he his birth was announced as the ushering in of the era of peace (cf. Luke 2:1-14)?
Jesus spoke the above words in the backdrop of the sending of the disciples on mission. Their period of “apprenticeship” having come to a close, it was now time for the twelve to put to practice what they had learnt. Although the twelve had always accompanied Jesus ever since they joined him, up until now they had only watched from the sidelines as Jesus proclaimed the good news of the kingdom by word and deed. But time had now come for them to become proclaimers and ministers of the good news. Unfortunately for them, they were going to be on their own. Being their maiden mission, this was going to be the make or break moment for the disciples. Jesus knew as much and in his commissioning speech, he made sure that the twelve were aware of what was awaiting them in mission. The twelve had to know that the message they had been charged with proclaiming was not going to be welcome by everyone. Due to its counter-cultural nature, their message was going to challenge the status quo by advocating for change of lifestyle, attitudes and behaviors that are not in conformity to the Gospel values. It is this nature of their proclamation that would end up exposing them to ridicule, rejection, and even persecution from some quarters. 
Jesus was not boasting about the division that his presence would cause in households. I believe the thought of a family breaking up on account of his message hurt him the most. If it was left to him, he would have wished that an entire household accept his message and get converted. However, he was also a realist. He already had the experience of being rejected in some quarters. Until the blazing fire of the Holy Spirit sweeps over the earth and changes the hearts of people, the divisions would continue. It was a fact that distressed him, but there was nothing he could do. He had to wait until his own baptism (death) before the entire world becomes ready for the baptism by the Holy Spirit whom he will send. Until the entire world is baptized with the Holy Spirit, proclaimers of the values of the kingdom must be prepared to be met with rejection and persecution. This was the message he wanted the disciples to take with them on their maiden mission.