If you want peace, prepare for war.
Let me start by saying that I detest war. I can not stand it! Rather funny seeing as I am in the military; but I live by the saying, "Si vis pacem para bellum" because it rings so true.
The war part is not always about bloodshed though, it can be about internal struggles as well. Take my roommate and I for instance; he loves country music, and I really don't care for the stuff, but to maintain peace in our room I get over my dislike for country music and let him listen to it - even though I want to ram a stake through my head.
Also, take marriage as another example. The average couple argues about stuff constantly; the two parties are like North and South Korea living in the DMZ! Do they want to fight and argue? Not most people, but it is hard for some people to compromise and concede to the other person to live peacefully. Even through compromise one is at war with themselves as they strive not to break the newly set guidelines.
Now, let us move to the spiritual side of things. If you want peace, prepare for war. Literally. Trying to live the Christian life is a daily struggle for many people; imagine if you will trying to keep a strict prayer rule, and a strict fasting rule, it can be very tedious! I know many people say don't try to just jump right in and do everything all at once (i.e. a strict prayer and fasting rule), but even taking that advice it can still be very hard to start praying and fasting as a Christian should.
Also, still on the spiritual side, we have the world and her influence to contend with every day - TV, internet, radio, friends, and family. It can be very tiring to try to push off those influences, but if you struggle through it - if you pick up your cross daily - you will reach the peace you seek.
So, since I believe that we must prepare for war when we seek peace, remember to keep your eyes on the prize - keep that finish line in your mind's eye - and never lose focus so you can win the battle and obtain peace.