Whatever may have been the case at other epochs of the history of the Church, it is clear that today treatments of confined topics of theology which can afford to take for granted theology and Christianity as a whole are no longer possible. This is true in a special way of the topic which concerns us here, the theology of the priesthood and the ministry, since we have to examine an essential element in the structure or form of Christianity itself, and since we are making this examination not as detached observers but as people who are considering the fundamental sense of our own lives.

Consequently it seems suitable to make explicit two presuppositions of what is to be said later. Firstly, Christianity is real. That is to say, it is real not only with the kind of reality which will allow it to be included among other realities in accordance with a scale of reality already set up apart from Christianity itself. Christianity is real in the sense that its reality modifies the scale of reality itself. Whether we say that Christianity is a new reality in a world considered as being without it (say, as being prior to it, or posterior to it, hostile or neutral to it), or whether we say that Christianity has always been and still is ‘anonymously’ present in the world (as, say, prefigured in a total history of humanity within the eternal design of God), we must, in terms of Christianity itself, claim that Christianity is at the very least a dimension of reality which needs explicitly to be taken into account if the ontological scale which we use to assess it and indeed anything else is to function as a true criterion of the real.