On the Divine Institution of The Papacy

That “feed my sheep” was said by Christ to Peter alone, the text itself clearly makes manifest: both from his own proper name and that of his carnal father, repeated a third time; and from the comparison set against the others, “lovest thou me more than these” — for the comparative shows his difference from the other apostles present, to whom he is compared; and from Peter's own suffering, whereby he is described as grieved at the third questioning, mindful of the denial of Christ once foretold to him when he himself was ready to die: so that no place is left for doubt. And since these things were given to Peter after the Lord's resurrection, and to the other apostles nothing similar is found to have been said either before or after, it remains that “feed my sheep” was said altogether to Peter alone.

Nor does it stand in the way that the Church, in the Preface, calls all the apostles shepherds of the Lord's flock (whom thou hast granted to the same flock, as vicars of thy work, to preside over it as shepherds), since this manifestly refers to the apostolate: and therefore they are called shepherds of the Lord's flock in that manner in which pastoral care pertains to the apostolate. But, as the very name “apostle” attests, the pastoral exercise belongs to the apostles as to legates of Christ: and thus it is that, as legates of Christ, they are called shepherds of the Lord's flock. But Peter (as will be clear from what has been said above and what is yet to be said) was appointed as the ordinary shepherd even of the apostles themselves: and this is what Christ's words “feed my sheep” signify.