Understanding Papal Infallibility
“Where Peter is, there is the Church.” — St. Ambrose of Milan
Definition (Vatican I, 1870):
Papal infallibility is the doctrine that the Pope, when speaking ex cathedra (from the Chair of Peter) on matters of faith and morals, is preserved from error by the Holy Spirit. Not personal sinlessness or infallibility in all actions or opinions.
1 Tim 3:15
But if I should be delayed, you should know how to behave in the household of God, which is the church of the living God, the pillar and foundation of truth.
The Catholic doctrine of infallibility holds that the Pope, when speaking ex cathedra (from the Chair of Peter) on matters of faith and morals, is preserved from error by the Holy Spirit. This teaching is rooted in Scripture and Tradition. Jesus promised Peter (the first Bishop of Rome (i.e. Pope)), “You are Peter, and on this rock I will build my Church, and the gates of hell shall not prevail against it” (Matthew 16:18)
The authoritative role, called “chair” was no new concept to Jesus. In Matthew 23, Jesus refers to the “Chair of Moses” as the teaching authority that Jewish followers were obliged to obey. Given the appointment of Peter in Matthew 16, which echos of the appointment of Eliakim in Isaiah 22, we have a new Office of Steward, the Chair of Peter.
Peter is Regarded as the Leader of the 12
2. Luke 22:31–32
"I have prayed for you [Peter] that your faith may not fail; and when you have turned again, strengthen your brethren."
Christ prays specifically for Peter’s faith not to fail.
3. John 21:15–17
"Feed my lambs… Tend my sheep…"
Christ entrusts the universal flock to Peter alone.
Jesus changes Simons name to Peter (meaning Rock). Throughout Scripture, when God changes your name, you take on a significant new role in serving God.
Jesus Commissions Simon/Peter using language from Isaiah
The connection between Matthew 16:18–19 and Isaiah 22:20–22 is deeply rooted in the biblical concept of authority, particularly royal and divine authority, and is central to the Catholic understanding of the papacy.
Matthew 16:18–19 (Jesus to Peter)
“And I tell you, you are Peter, and on this rock I will build my Church, and the gates of Hades will not prevail against it.
I will give you the keys of the kingdom of heaven, and whatever you bind on earth shall be bound in heaven, and whatever you loose on earth shall be loosed in heaven.”
Isaiah 22:20–22 (Prophecy about Eliakim)
“In that day I will call my servant Eliakim son of Hilkiah...
I will clothe him with your robe...
I will place on his shoulder the key of the house of David;
he shall open, and none shall shut;
and he shall shut, and none shall open.”
Key Parallels and Connections
Theme Isaiah 22 Matthew 16 Authority Given by God God appoints Eliakim Jesus appoints Peter Key Symbolism "Key of the house of David" (symbol of royal authority) "Keys of the kingdom of heaven" (authority in the Church) Power to Open and Shut "He shall open, and none shall shut..." "Whatever you bind... loose..." Royal Stewardship Eliakim is given the office of royal steward (prime minister) under the king Peter is given a governing role under Christ the King
Catholic Interpretation
In ancient Israel, the king (like David) had many officials, but one chief steward held the "key of the house of David"—a symbol of delegated authority.
Isaiah 22 is the only Old Testament passage explicitly mentioning this key and the power to open and shut.
Jesus, the Son of David, alludes directly to this passage when giving Peter the keys of the kingdom.
This suggests that Peter is being appointed as the chief steward or prime minister of Jesus' Kingdom—what Catholics recognize as the first pope.
Matthew 16:18–19 echoes Isaiah 22:20–22 to establish a biblical precedent for conferring authority through the giving of keys, showing that Jesus intentionally used language tied to royal stewardship to appoint Peter as the earthly leader of His Church. This typological link strongly supports the Catholic doctrine of the papacy.
Historical Development
Infallibility was always believed implicitly, but defined explicitly in 1870.
The Magisterium’s role: clarify and define what was always taught.
Reference: Lumen Gentium (Vatican II), no. 25
Support from Early Church Fathers
St. Irenaeus of Lyon (c. 180 A.D.)
“It is a matter of necessity that every Church should agree with this Church [Rome], on account of its preeminent authority.”
— Against Heresies 3.3.2
St. Cyprian of Carthage (c. 250 A.D.)
“The Chair of Peter, the principal Church, whence Episcopal unity has arisen…”
— Epistle 59:14
St. Augustine (c. 400 A.D.)
“Rome has spoken; the case is closed.”
— Sermon 131
Pope St. Leo the Great (c. 450 A.D.)
“The faith of Peter... cannot fail... and what Peter believed, that the Church believes.”
— Sermon 82
Clarifying Infallibility
Conditions for Papal Infallibility:
Pope must speak ex cathedra (from the Chair of Peter).
The subject must be faith or morals.
The intent must be to define a doctrine to be held by the whole Church.
Examples of Ex Cathedra Declarations:
1854: Immaculate Conception (Ineffabilis Deus)
1950: Assumption of Mary (Munificentissimus Deus)
Common Objections Answered
Objection: “There were bad popes — how can they be infallible?”
Answer: Infallibility is not the same as impeccability. Even sinful popes can be protected from teaching error in specific circumstances.
Objection: “The doctrine was invented at Vatican I.”
Answer: No — it was defined at Vatican I but supported by Scripture and consistently upheld by Tradition.
Theological and Practical Importance
Ensures unity of doctrine.
Provides certainty in moral and theological questions.
Preserves apostolic teaching from corruption.
Catechism of the Catholic Church, 891:
“The Roman Pontiff… enjoys this infallibility in virtue of his office…”
References
Primary Sources:
Holy Bible (Matt. 16, Luke 22, John 21)
Catechism of the Catholic Church, §§ 880–891
Pastor Aeternus, Vatican I
Lumen Gentium, Vatican II
Early Church Fathers:
St. Irenaeus, Against Heresies
St. Cyprian, Letters
St. Augustine, Sermons
Pope Leo the Great, Sermons
Modern Apologetics:
Ludwig Ott, Fundamentals of Catholic Dogma
Karl Keating, Catholicism and Fundamentalism
Scott Hahn, Rome Sweet Home