Thomas Cranmer was Archbishop of Canterbury (1533-1556) in the reign of Henry VIII and Edward VI. He was deposed under Mary Tudor and burned at Oxford as a heretic. The charges brought against him were based chiefly on the doctrine of the Lord's Supper expounded in this book.
The core of Cranmer's teaching was that the sacrament was essentially spiritual in nature. The body of Christ was not present in a physical or carnal way, as the Church of Rome taught by its doctrine of transubstantiation. Cranmer based his position on Scripture, in particular St. John's Gospel, where, he showed, Christ meant eating and drinking His body and blood to be understood as receiving by faith the benefits of His death for sins. To think of eating and drinking Christ's actual body and blood with the mouth is, he argued, a gross misunderstanding; the purpose of the sacrament is to satisfy spiritual hunger.
The Roman doctrine, he maintained, was also contrary to the true Catholic teaching of the two natures of Christ - His humanity and His divinity. In the creeds we confess that Christ has ascended bodily into heaven, not to return to earth in that manner until the last day. The true Catholic faith, therefore, requires us to believe that He is not present with us in the nature of His humanity but that He is present in the nature of His deity. To teach, as the Church of Rome does, that He is present bodily in the sacrament is to deny this teaching of the creeds, to assert a heretical doctrine of the one nature of Christ and to deny His real humanity. For this reason Cranmer called his book 'A Defence of the True and Catholic Doctrine of the Sacrament'. The errors of Rome also extended to the notion that the sacrament was a sacrifice offered by the priest to take away sins. Cranmer refuted this from the Scriptures and the ancient Fathers.
