A peaceful spirit arises from a pure heart. But it is not enough to be peaceful. The one who is blessed is one who seeks to bring peace. Especially where there is no peace. The peacemaker is one who looks for ways to reconcile those around him (or her). When the matter becomes particularly heated, the peacemaker steps in and suffers the blows as Christ stepped in for those He came to redeem.
But what about that sister . . . or boss . . . or roommate . . . or neighbor? The one you tried making things right with, and it just didn't work. I love how C.S. Lewis put it:
You know, in fact, that any attempt to talk things over with "X" will shipwreck on the old, fatal flaw of "X's" character . . . but when God looks into your home or factory or office, He sees one more person of the same kind - the one you never do see. I mean, of course, yourself. That is the next great step in wisdom - to realize that you also are just that sort of person. You also have a fatal flaw in your character. All the hope and plans of others have again and again shipwrecked on your character just as your hope and plans have shipwrecked on theirs.
That is one way in which God's view must differ from mine. He sees all the characters: I see all except my own. But the second difference is this. He loves the people in spite of their faults. He goes on loving . . . The more we can imitate God in both these respects, the more progress we shall make. We must love "X" more; and we must learn to see ourselves as a person of exactly the same kind.
To be a peacemaker requires personal risk. It is to put one's own wellbeing, reputation, and life on the line to be a reconciler.
And when we put it on the line, we begin to reflect God's character!