Saint John Fisher held the primacy of the pope to be so much a divinely-established principle of Christian unity as to lay down his life in its defense. He tried to protect that unity at all cost because it manifested in his eyes the unity of life which is established between God and man through the reception of the sacraments, all pivoted on the Eucharistic sacrifice as celebrated by priests. Fisher’s sustained argument on behalf of the sacramental priesthood, which Luther was resolved to void of its meaning, therefore goes hand in hand with Fisher’s defense of the unity of the Church, which is embodied in its priestly or hierarchical organization, resting on Peter and his successors. In these ecumenical times Fisher’s book should be a sober reminder about some basic spiritual realities that for the backbone of the Church as established by Jesus Christ. In the Introduction by Father Stanley L. Jaki, Saint John Fisher’s book is put into the context of one of the greatest ecclesiological contestations the Church has had to face.