If the first millennium of Christianity was marked by the substantial unity of the Church, and the second millennium was the era of Christian division, what does the third millennium hold? Will it be the time of the restoration of the unity of the Church of Jesus Christ? Is this an unrealistic expectation? No, Christians hope for unity because at the Last Supper Jesus Himself prayed for all who would believe in Him: ‘that they may all be one [‘utunumsint’]; even as you Father are in me, and I in you…’ (Jn. 17:21).

Before undertaking our review of Pope John Paul II’s twelfth encyclical letter Ut Unum Sint issued on May 25, 1995, it would be helpful to establish the context for this encyclical by discussing the emergence of the ecumenical movement and the teaching on ecumenism of the Second Vatican Council. One evident fruit of Jesus’ prayer for unity in our time is the emergence of the ecumenical movement at the beginning of the 20th century. The Second Vatican Council’s ‘Decree on Ecumenism’ (Unitatis Redintegratio, 1964, henceforth UR) defines ecumenism as ‘…a movement, fostered by the grace of the Holy Spirit, for the restoration of unity among all Christians’ (UR 1). This movement gathered support when Protestant missionaries met and discussed the scandal of Christians contending for converts in mission lands, all claiming to be the ‘true church’ or to preach the full gospel of Jesus Christ. The Catholic Church did not become involved in the Protestant and Orthodox ecumenical efforts based on the same claim that the Catholic Church was the one, true Church. In this view the only legitimate ecumenism was for the Christians who had broken from the Catholic Church to return to her. This was the position of Pope Pius XI in his 1928 encyclical letter, Mortalium Animos.