Pope John understood that avoiding war was a noble objective but building peace was something else altogether. He said that to forge genuine and lasting peace required nations to build societies on foundations of truth, charity, justice and human rights. To do that required a fundamental shift from the Cold War mentality of maintaining a fragile peace by threat of mutual destruction to building an enduring peace through the universal promotion of the common good.

At the time of writing, Pope John was dying of cancer. He knew Pacem in Terris (Peace on Earth) would be his only chance to address this issue. It was a time of considerable tension in East-West relations following the rise of the Berlin Wall and the Cuban missile crisis that took the superpowers to the brink of war. In fact, Pacem in Terris began as a letter from the Pope to American President John Kennedy and Soviet Premier Nikita Krushchev, urging them to resolve the 1962 dispute over Cuba.

The Pope’s message was broadcast on Vatican Radio and published in newspapers worldwide and was credited with helping restore calm. Time magazine recognized the Pope’s contribution by naming him Man of the Year.

Six months later, his letter was transformed into a ground-breaking encyclical that called for the end of the arms race and a ban on nuclear weapons. But Pacem in Terris was much more than a treatise on nuclear disarmament. It outlined a radical model for peace based on principles of equality, dignity, freedom and justice, and the advancement of universal human rights. The message to Catholics was that peacemaking on these terms was fundamental to Christian faith. But Pope John also reached out to non-Catholics, to “all men of goodwill,” to believers and non-believers who craved a social order that promoted human dignity.

Rare for a papal encyclical, Pacem in Terris was embraced far beyond the Catholic world. It was studied at the United Nations, published by the Soviet news agency Tass and its author was lauded in the Washington Post as “the conscience of the world.” It became a blueprint for advancing human rights, freedom and peace, and impacted the thinking and writing on these topics for years to come.

Pope John died two months after the encyclical was published. Fifty years later, the Cold War is long gone but it has been replaced by other impediments to world peace. So Pope John’s vision and his words in Pacem in Terris remain as important today as they were in 1963.