A phrase I often hear my Christian friends repeat when facing the struggles of life is "I don't know how unbelievers do it". As human beings, we tend to base our peace on our situation. When things are going well, we're happy and at peace. When things aren't going so well, we feel like the world is ending around us.
Christians have a natural advantage in this area. Obviously, we're not perfect. It's not like we can calmly walk into a war zone singing "Amazing Grace" with our arms wide open and a strange, cartoonish aura behind us with butterflies fluttering everywhere. We still feel the anguish of loss, pain, even mental illness. But we do have the added bonus of having a well-grounded hope. We know that God Himself cares about our struggles, and His divine hand is on them.
We also know that not even death is really a loss for a believer. As Christians, we can lie on our death beds and know that whether we are young or old, rich or poor, eternity is just beginning. And this time around, we aren't going to be sinning, suffering as a result of sin, or separate from God. Rather, we will know Him face to face.
As a result of this, our peace is actually immutable. Imprisonment, beatings, persecution, even martyrdom, have all been very serious threats to the Church since Christ established it, and yet even as the martyrs died, they were able to bless their enemies! This, my brethren, is the God we serve. A God so powerful, so loving, that nothing short of actual separation from Him, which is impossible for a true believer, can destroy our peace.