One of the primary motivations for John XXIII to call the Second Vatican Council was ecumenical. He took stock of 20th Century Europe and realized that Christianity had failed the world. While the Protestants and Catholics had been more or less bickering, two world wars had occurred, and the churches, both Catholic and Protestant, had failed to give aid fully. The Body of Christ was splintered, and movements towards unity — but not uniformity — were needed.

In order for ecumenical activities to take place, it was necessary to clarify the teachings of the Roman Catholic Church, which consisted largely of stripping away layers of "historical varnish" and return to the bare basics of the early Church.

In this regard, the Second Vatican Council was not as revolutionary as many have perceived it to be. While 20th Century theologians – notably Karl Rahner and Bernard Lonergan – provided the theological underpinnings for the council, Sacred Scripture and the Patristic Writings were the primary texts drawn upon in the drafting of the sixteen documents of the Council.

As to the turmoil within the Church as a result of the Second Vatican Council, it was something to be anticipated: historically, any time there was a major ecumenical council within the Roman Catholic Church, major upheaval followed. Conventional wisdom holds that three generations will be "lost" before stability returns and the full-flowering of the Council occurs.