The general secretary of the World Council of Churches, Rev. Olav Fykse Tveit, has sent a letter expressed "profound thanks" to Pope Benedict XVI for his contribution to Christian unity.

"On the occasion of your resignation from the Apostolic See of Rome and the Petrine ministry, we in the ecumenical movement pause to recall your many contributions to the life of the Church and the world, and to wish you well as your ministry of prayer and meditation continues," said Tveit in his Feb. 27 letter.

Benedict makes history on Thursday when he will become the first pope to voluntarily resign in 600 years.

Tveit noted Benedict's engagement with the world council's Commission on Faith and Order when he was Joseph Ratzinger and a Catholic professor of theology in 1971.

The World Council of Churches promotes Christian unity and brings together 349 Protestant, Orthodox, Anglican and other churches representing more than 560 million Christians.

The Roman Catholic Church is not a member of the WCC but works cooperatively with the council and serves on its Commission on Faith and Order, which seeks to find common theological areas between different churches and denominations

"In looking from an ecumenical perspective over your entire service to the church, the World Council of Churches is grateful for your devotion to the quest for Christian unity as a pattern for the unity of all humanity," Tveit stated..

Tveit mentioned Benedict's "partnership in ministry" from which, he said, the WCC has benefited.

He also expressed thanks for the Pope's support to Catholic representatives in WCC events, the Joint Working Group between the Roman Catholic Church and the WCC, the Faith and Order Commission, the Commission on World Mission and Evangelism, Tviet also cited cooperation with Catholics in other initiatives such as the Global Christian Forum.

The Norwegian Lutheran who heads the WCC remembered his meetings with Pope Benedict in Rome, 2010, and at the Day of Prayer for Peace in the World in Assisi, 2011.

Tveit said, "Our conversations have left me with a conviction of the importance of strengthening already strong relations that enable Christians of many backgrounds to pray together, work together and rededicate ourselves to unity in faith."