Finally, the Holy Fathers teach unanimously not only that heretics are outside of the Church, but also that they are “ipso facto” deprived of all ecclesiastical jurisdiction and dignity. St. Cyprian (lib. 2, epist. 6) says: ‘We affirm that absolutely no heretic or schismatic has any power or right’; and he also teaches (lib. 2, epist. 1) that the heretics who return to the Church must be received as laymen, even though they have been formerly priests or bishops in the Church. St. Optatus (lib. 1 cont. Parmen.) teaches that heretics and schismatics cannot have the keys of the kingdom of heaven, nor bind nor loose. St. Ambrose (lib. 1 de poenit., ca. 2), St. Augustine (in Enchir., cap 65), St. Jerome (lib. cont. Lucifer.) teach the same.
Therefore, the true opinion is the fifth, according to which the Pope who is manifestly a heretic ceases by himself to be Pope and head, in the same way as he ceases to be a Christian and a member of the body of the Church; and for this reason he can be judged and punished by the Church. This is the opinion of all the ancient Fathers, who teach that manifest heretics immediately lose all jurisdiction, and outstandingly that of St. Cyprian (lib. 4, epist. 2) who speaks as follows of Novatian, who was Pope * in the schism which occurred during the pontificate of St. Cornelius: 'He would not be able to retain the episcopate , and, if he was made bishop before, he separated himself from the body of those who were, like him, bishops, and from the unity of the Church.’*
The foundation of the encyclical Mystici Corporis was the teaching of St. Robert Bellarmine which was based on the visibility of the Church.
SFD