I have come to bring not peace but division. If Peter had thought that Jesus’ earlier statement on the need to be vigilant was asking too much from them (cf. 12:41, yesterday’s Gospel Reading), he was grossly mistaken. Jesus was not finished yet. In today’s passage, Jesus continues the conversation as he opens the eyes of the disciples to the reality of the ministry for which they had signed up. Because of the demands the Gospel message places on its hearers, the disciples needed not to be alarmed in case they were to encounter some resistance along the way since not everyone was going to embrace their message with open arms. As a matter of fact, the disciples needed to be prepared for such a mixed response since their master expected nothing less: “My message will set a son against his father and a daughter in law against her mother in law.”
How can we reconcile the above statement of Jesus with the fact that he is the prince of peace? Wasn’t his birth announced as the ushering in of an era of peace (cf. Luke 2:1-14)? Why wouldn’t a bringer of so much needed peace be rejected? Jesus is indeed the prince of peace, and his birth did usher in an era of peace. And even as Simeon had prophesied that the baby Jesus was to be a sign that will be opposed as he would lead to the rise and fall of many (cf. Luke 2:33-34), Jesus brought to the world the gift of peace, a peace that the world had hitherto not known (cf. John 14:27). 
In the Gospel according to Matthew, Jesus made the above statement in the context of him giving instructions to those whom he was to send on mission (cf. Matthew chapter 10). Jesus did not want to beat about the bush about what awaited them in the field. He was not issuing the statement in order to scare the disciples but rather to prepare them for what was lying ahead of them. The message that Jesus wanted them to bring to the ends of the earth was not going to be welcome by everyone. It was a message that was not only going to challenge its hearers but was also going to demand something from them. It was a message that was going to challenge the status quo even as it championed change. Those who are disposed to the kingdom that Jesus was ushering in would readily welcome the message of Jesus whereas those who are not of the kingdom would oppose the message. This is how the division that Jesus talks about would come about.