Although the Roman Catholic Church does not belong to the World Council of Churches itself, it is actively engaged in extensive discussion and collaboration with other churches and communions which belong to it. Indeed it is a full, active member and partner with the World Council members of the Commission on Faith and Order.
But why, given the leading role of Catholics and the Catholic Church in promoting the path to unity, is the Catholic Church not a full member of the World Council of Churches itself? Or ask the question another way round: why is the World Council of Churches not a member of the Catholic Church?
As the Catholic Church believes that in Baptism God has already given complete unity to all Christians, it also believes that the universal Church of Christ is one from its roots. So it does not accept that Christianity is or can be 'many' separate churches, each representing the one Church of Christ but with varying kinds of structure and differing forms of teaching. The Catholic Church believes that the one Church of Christ is organised in a visible living organ in this world by Christ’s commission to St Peter and the apostles and that it is the Catholic Church’s belief and structure which completely embody that. That is not to say that many elements of the one Church of Christ, its truth, holiness and the way it is ordered, are not to be found beyond the structures of the Catholic Church. Far from it: these gifts belonging to the whole Church of the baptised are to be found in abundance among other Christian churches and communities, and motivate it to recover its unity and integrity as one Church in this world.
But Catholics believe that the whole of our belief, including the unique ministry of the Pope as successor to St Peter and of all the bishops as successors to the Apostles, is essential to the unity of the one visible Church of Christ. Formally joining the World Council of Churches could signal that the Catholic Church is prepared to accept that the core of faith is only what all Christians can agree on, the highest common factor, to which the rest of our Catholic faith, Church structure and sacramental life, is additional or even optional.
There are many different ways of being the Church – different rites and orders, distinctive and diverse traditions and – but these cannot in the end remain separate from each other. It is the nature of the universal Church in all its richness and diversity to be for all, and not dividing into different followings. So the Catholic Church, as not only part of but also the fullest expression of the one Church of Christ, feels that membership of the World Council of Churches could compound the sin of division and formalise separation, rather than transcend it.
The witness of the Catholic Church is therefore that all Christians together need to work patiently but relentlessly to find agreement and reconciliation, not only in what others believe, but also in what Catholics believe. This is why the Catholic Church is fully committed to belonging to the Commission on Faith and Order along with members of the World Council of Churches. It is also why for decades it has been in sustained dialogue with other Churches and Ecclesial or Church Communities to achieve this agreement and reconciliation. Indeed the active and official involvement of the Orthodox and Catholic Churches in the ecumenical movement has meant that the unity of faith and Church life in terms of communion has become a much stronger focus for all churches and ecclesial communities. This has meant considerable progress in the various bilateral conversations among the churches - including the resolution of historic disagreements and even occasions for sharing the Eucharist.
The Catholic Church, believing that perfect reconciliation in faith is integral to the unity of the Church, recognises that the ecumenical journey can be painstaking and will need time. But it trusts absolutely that the unity of the One Church will be revealed by Christ at the moment of his choosing, as Paul Couturier said, 'according to his will, according to his means.'