“Blessed are the peacemakers, for they shall be called sons of God” (Matthew 5.9).
Jesus pronounces this blessing in His first recorded sermon in what are called The Beatitudes when He is speaking to the multitudes on the mountain. He is teaching these people some of the characteristics of those who will become a part of His coming kingdom.
To be a peacemaker is quite different from living peaceably. A peacemaker is one who brings about peace or, at least, one who actively works to reconcile others who are not at peace. Jesus Himself is the Prince of Peace; so, it is only fitting that His followers serve as agents to help others find peace.
This passage places the role of peacemaker at the top of any list: all serious spiritually-minded people want to be called a son (or a daughter) of God; thus, we must take to heart this challenge to be a peacemaker.