Matthew 10:34

Some quote verses like John 14:27 as a contradiction to this verse: "Peace I leave with you, my peace I give unto you: not as the world giveth, give I unto you. Let not your heart be troubled, neither let it be afraid." The perceived contradiction comes from a misunderstanding of the word "peace" as used in the New Testament. If the word "peace" is to be defined as an absence of conflict, the second clause of this sentence is contradictory to the first. Jesus would not need to encourage his audience to resist fear and trouble if he would be leaving them with a lack of conflict. Clearly Jesus is promising his followers a peace in the presence of conflict, to carry them through the coming trials.

http://en.wikipedia.org/wiki/But_to_bring_a_sword