The true Church is a believed Church; in a real sense we have to ‘believe’ the Church, for the Church can only be recognised in its essential nature through faith. Yet the Church as the ‘called out’ community of the faithful is not simply invisible; it is both visible and invisible. As the people of God, the Church is essentially a ‘people’, and thus is visible. As the body of Christ, the Church is a ‘body’, and thus is visible. In the concrete visible Church there is a mixture of wheat and tares.’ Because the Church consists of human beings, and sinful human beings, renewal and reform of the Church is always necessary. In every age and generation she is faced with the task of presenting herself anew. It is with this understanding of the constant renewal of the Church — ecclesia semper reformanda — that we approach our subject.

The Unity of the Church is not primarily a unity of members among themselves, but is essentially a given unity which has its origin in God himself in his triune being of Father, Son and Holy Spirit. This unity was actualized in Jesus Christ himself and made efficacious in the Holy Spirit. The whole New Testament message bears witness to this unity of origin. The classic texts are well known: 1 Cor 1: 10-30; 1 Cor 12; Gal 3: 27f; Rom 12: 3-8; Acts 2:42; 4: 32; John 10: 16; 17; 20-26; Eph 4: 1-6. There was indeed a consciousness of unity everywhere, and it was this consciousness of unity which was one of the factors which constituted the Church. This consciousness of unity became an essential element in the Church’s self-definition, as one of the four characteristics of the Church set out in the Nicene Creed: ‘We believe one, holy, catholic and apostolic Church’.