It is a grievous offense willfully to conceal a mortal sin in Confession, because we thereby tell a lie to the Holy Ghost, and make our Confession worthless.
"There is also the superstition of the Ishmaelites which to this day prevails and keeps people in error, being a forerunner of the Antichrist."
"[H]aving forbidden all unlawful marriage, and all unseemly practice, and the union of women with women and men with men..."
"And I will place on his should the key of the house of David; he shall open, and none shall shut; and he shall shut, and none shall open. And I will fasten him like a peg in a sure place, and he will become a throne of honor to his father’s house."
"Seeing the dignity to which the humble are raised, and the deep abyss into which the proud fall, let us imitate the virtue of the Publican, and despise the sins of the Pharisee."
"O Holy Head, Christ our God hath destined thy Apostolic See to be an immovable foundation and a pillar of the Faith. For thou art, as the Divine Word truly saith, Peter, and on thee as a foundation-stone have the pillars of the Church been fixed."
"Since to great Peter Christ our Lord gave the office of Chief Shepherd after entrusting him with the keys of the Kingdom of Heaven, to Peter or his successor must of necessity every novelty in the Catholic Church be referred. [Therefore], save us, oh most divine Head of Heads, Chief Shepherd of the Church of...
"In the power of the same Holy Spirit, Peter, also the foremost of the Apostles and the key-bearer of the Kingdom of Heaven, healed Aeneas the paralytic in the name of Christ."
Cyril, Catech. xviii. n. 27
The importance of establishing St. Peter's ministry in Rome may be boiled down to authority and more specifically the historic existence and continuance of the Office of Vicar held by St. Peter.