3. In the light of the foregoing, it is understood that the diaconia peculiar to Peter and his successors is necessarily related to the diaconia of the other apostles and their successors, whose sole purpose is to build up the Church in this world.

From ancient times, this essential and interdependent relation of the Petrine ministry with the task and ministry of the other apostles has demanded something of a visible sign, not just by way of a symbol but something existing in reality, and it must still demand it. Deeply conscious of the burden of apostolic toil, our predecessors have given clear and thoughtful expression to this need, as we see, for example, in the words of Innocent III who wrote to the bishops and prelates of France in 1198 when he was sending a legate to them: "Although the Lord has given us the fullness of power in the Church, a power that makes us owe something to all Christians, still we cannot stretch the limits of human nature. Since we cannot deal personally with every single concern — the law of human condition does not suffer it — we are sometimes constrained to use certain brothers of ours as extensions of our own body, to take care of things we would rather deal with in person if the convenience of the Church allowed it."

This gives some insight into the nature of that institution that Peter’s successor has used in exercising his mission for the good of the universal Church, and some understanding of the procedures by which the institution itself has had to carry out its task: we mean the Roman Curia, which has worked in the service of the Petrine ministry from ancient times.

For the Roman Curia came into existence for this purpose, that the fruitful communion we mentioned might be strengthened and make ever more bountiful progress, rendering more effective the task of pastor of the Church which Christ entrusted to Peter and his successors, a task that has been growing and expanding from day to day. Our predecessor Sixtus V, in the Apostolic Constitution Immensa æterni Dei, admitted as much: "The Roman Pontiff, whom Christ the Lord constituted as visible head of his body, the Church, and appointed for the care of all the Churches, calls and rallies unto himself many collaborators for this immense responsibility [...]; so that he, the holder of the key of all this power, may share the huge mass of business and responsibilities among them — i.e., the cardinals — and the other authorities of the Roman Curia, and by God’s helping grace avoid breaking under the strain."