Pacem in Terris is an encyclical, and its argument for world peace invokes several Christian themes of nonviolence and pacifism. Proponents of pacifism find scriptural basis for nonviolence in Jesus’ message of forgiveness, compassion, and in his unwillingness to resort to physical violence, even in instances of defense.

The section on disarmament, in which Pope John argues for the necessity of ceasing all warfare in the nuclear age, is an argument built on the concept of just-war teachings. Just-war teachings delineate the criteria in which war may be morally justified or necessary. The seven criteria are as follows: just cause, competent authority, last resort, comparative justice, proportionality, right intention, and probability of success. However, warfare as destructive and undiscriminating as nuclear warfare, which would kill thousands of civilians and leave monumental devastation in its wake and possibly precipitate an even more catastrophic nuclear response, cannot be justified under the seven tenets of just-war theory.

The Catholic Church also has a rich history of actively promoting and teaching social justice, and Pacem in Terris takes part in this history in its fervent advocacy of the special dignity and rights of the individual human being as a child of God. The ecumenical nature of the encyclical demonstrates that Jesus’ message of peace, compassion, and love transcends national, political, religious, and social boundaries and exhorts unity and equality among all people. Pope John, throughout Pacem in Terris, builds on the teachings of both biblical Scripture and previous popes, particularly those of his immediate predecessor, Pius XII, establishing Pacem in Terris as firmly rooted in Catholic theology.