77 In our generation when men continue to be afflicted by acute hardships and anxieties arising from the ravages of war or the threat of it, the whole human family faces an hour of supreme crisis in its advance toward maturity. Moving gradually together and everywhere more conscious already of its unity, this family cannot accomplish its task of constructing for all men everywhere a world more genuinely human unless each person devotes himself to the cause of peace with renewed vigor. Thus it happens that the Gospel message, which is in harmony with the loftier strivings and aspirations of the human race, takes on a new luster in our day as it declares that the artisans of peace are blessed "because they will be called the sons of God" (Matt. 5:9). Consequently, as it points out the authentic and noble meaning of peace and condemns the frightfulness of war, the Council wishes passionately to summon Christians to cooperate, under the help of Christ the author of peace, with all men in securing among themselves a peace based on justice and love and in setting up the instruments of peace.
Source: Gaudium et Spes (Vatican.va)