The primary purpose of the fellowship of churches in the World Council of Churches is to call one another to visible unity in one faith and in one eucharistic fellowship, expressed in worship and common life in Christ, through witness and service to the world, and to advance towards that unity in order that the world may believe.

Almost from the beginning, divisions were present among the followers of Jesus Christ. So was, however, the vision of perfect unity, spelled out in the Nicene Creed as the "one, holy, catholic and apostolic church". That Christians should be divided by confessional lines and different understandings of the Scriptures is often referred to as the "scandal of division" because it contradicts Jesus' prayer for his disciples, recorded in the Gospel of John: "that they may all be one (…) so that the world may believe." While the unity of the church is a goal yet to be realized in history, it is already a God-given reality on the spiritual level. The ecumenical task, then, is to manifest this oneness, to make it visible and effective.

Read the article on "unity" from the Dictionary of the Ecumenical Movement

The World Council of Churches encourages churches to pray for each other and with each other. It creates opportunities to learn from each other's traditions and insights, and to discuss differences.

The Message of the First Assembly in Amsterdam included this observation: "As we have talked with one another here, we have begun to understand how our separation has prevented us from receiving correction from one another in Christ. And because we lacked this correction, the world has often heard from us not the Word of God but the words of men." The church representatives pledged: "We intend to stay together."

Since its foundation in 1948 the WCC has helped churches to enter into radically changed relationships with each other, to reach agreements and convergences in basic issues of faith and ecclesiastical polity.

The constitutional commitment to unity finds its central expression in the work of the WCC Commission on Faith and Order. At the same time, all WCC activities should help the churches to effectively live out their existing fellowship and to move towards full visible unity.

Some examples:

• The Week of Prayer for Christian Unity
• The Ecumenical Prayer Cycle
• Study process on The nature and mission of the church
• Project Towards just and inclusive communities
• Living Letters visits to churches

Since the early stages of the modern ecumenical movement, there was debate on how to realize visible unity; different concepts and models were discussed. WCC assemblies and meetings of the other governing bodies, as well as the Faith and Order Commission, provided a platform to advance this debate.

Some examples:

• Called to be the One Church, adopted by the WCC 9th assembly in Porto Alegre, Brazil, 2006
• The Unity of the Church: Gift and Calling, adopted by the WCC 7th assembly in Canberra, Australia, 1991
• Nairobi statement 1975
• Uppsala statement 1968
• New Delhi Statement on Unity, WCC 3rd assembly, New Delhi, India 1961
• "The Church, the Churches and the World Council of Churches", WCC Central Committee, Toronto, Canada, 1950
• The Nature and Mission of the Church - A Stage on the Way to a Common Statement, Faith and Order Paper no. 198, 2005
• Costly Unity, Faith and Order study report, 1997
• Towards Sharing the One Faith - A Study Guide for Discussion Groups, Faith and Order Paper No. 173, 1996
• Final Statement from the Consultation "Ecumenism in the 21st century", Chavannes-de-Bogis, Switzerland, 2004
• Perseverance in Seeking Unity, address by WCC moderator Rev. Dr Walter Altmann, 2008
• Sermon on "The gift of Unity" by WCC general secretary Rev. Dr Samuel Kobia, 2007