But His All Holiness Bartholomew I, Ecumenical Patriarch of Constantinople, reminded the near-capacity congregation at Geneva's St Pierre Cathedral that the WCC has accomplished much in its six decades.
"The Council has provided an ideal platform where churches with different outlooks and belonging to a great variety of theological and ecclesiological traditions have been able to engage in dialogue and promote Christian unity, while all the time responding to the manifold needs of contemporary society," the Orthodox leader said, speaking in French.
He acknowledged the challenges and "turbulent" periods in the Council's life, but said that dialogue resulted from those difficulties and has paved the way forward. At the WCC's Ninth Assembly in Porto Alegre, Brazil, two years ago, "markers for a new stage in the life of the Council" were laid down, he said.
The Ecumenical Patriarch, often referred to as the spiritual leader of the world's Orthodox, said he envisioned a future that will enable "a new generation of labourers to flourish in the ecumenical vineyard" and that retains a foundation of the "three pillars" of unity, witness, and service on which the WCC was built.
The WCC, he said, has the opportunity to locate itself "at the centre of the life of the global ecumenical village" in the 21st century, and he urged it to "go forward with hope".
Earlier, in welcoming the crowd to "this very special occasion in this very special place", WCC President from North America Rev Dr Bernice Powell Jackson noted that the cathedral was an appropriate setting for marking the anniversary. It was, she said, "where the very first ecumenical service was held after World War II", in 1946.
The 90-minute service had an international flavour. The WCC's four working languages of English, French, German, and Spanish were all represented in music and word. The service also included a chorus in Greek, scripture readings in Swahili and Indonesian, and the upbeat music of the Valihan'i Jehovah Choirâ€"a group from the ecumenical community of Madagascar based in Switzerland. Young adult stewards serving at this week's Central Committee meetings provided leadership for the service.
The choir closed the service by singing the word "peace" in a variety of languages, concluding with the ringing of small cymbals. As guests exited, each received a small flower pot containing a candle as symbols that WCC members "are carrying the seed of peace and also the light of Christ which illuminates the world".
Numerous other church leaders were present at the service, including Bishop Brian Farrell, secretary of the Pontifical Council for Promoting Christian Unity; the Venerable Colin Williams, general secretary of the Conference of European Churches; Rev. Dr Setri Nyomi, general secretary of the World Alliance of Reformed Churches; Rev. Dr Ishmael Noko, general secretary of the Lutheran World Federation; and other Orthodox, Protestant, Roman Catholic, ecumenical, and government officials.