Here are a few quotes from Sunday Morning's Sermon:
J.C. Ryle: He means those who use all their influence to promote peace and love on earth, in private and in public, at home and abroad. He means those who strive to make all people love one another, by teaching the Gospel which says, ‘Love is the fulfillment of the law’ (Romans 13:10).
John Calvin: By peace-makers he means those who not only seek peace and avoid quarrels, as far as lies in their power, but who also labour to settle differences among others, who advise all men to live at peace, and take away every occasion of hatred and strife.
D. Martyn Lloyd-Jones: Why are peacemakers blessed? The answer is that they are blessed because they are the people who stand out as being different from the rest of the world, and they are different because they are children of God.