From: Matthew 16:13-19:

Peter's Profession of Faith and His Primacy

[13] Now when Jesus came into the district of Caesarea Philippi, He
asked His disciples, "Who do men say that the Son of Man is?" [14] And
they said, "Some say John the Baptist, others say Elijah, and others
Jeremiah or one of the prophets." [15] He said to them, "But who do
you say that I am?" [16] Simon Peter replied, "You are the Christ, the
Son of the living God." [17] And Jesus answered him, "Blessed are you,
Simon Bar-Jona! For flesh and blood has not revealed this to you, but
My Father who is in Heaven. [18] And I tell you, you are Peter, and on
this rock I will build My Church, and the powers of death shall not
prevail against it. [19] 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."

Commentary:

13-20. In this passage St. Peter is promised primacy over the whole
Church, a primacy which Jesus will confer on him after His
Resurrection, as we learn in the Gospel of St. John (cf. John
21:15-18). This supreme authority is given to Peter for the benefit of
the Church. Because the Church has to last until the end of time, this
authority will be passed on to Peter's successors down through
history. The Bishop of Rome, the Pope, is the successor of Peter.

The solemn Magisterium of the Church, in the First Vatican Council,
defined the doctrine of the primacy of Peter and his successors in
these terms:

"We teach and declare, therefore, according to the testimony of the
Gospel that the primacy of jurisdiction over the whole Church was
immediately and directly promised to and conferred upon the blessed
Apostle Peter by Christ the Lord. For to Simon, Christ had said, `You
shall be called Cephas' (John 1:42). Then, after Simon had
acknowledged Christ with the confession, `You are the Christ, the Son
of the living God' (Matthew 16:16), it was to Simon alone that the
solemn words were spoken by the Lord: `Blessed are you, Simon
Bar-Jona. For flesh and blood has not revealed this to you, but My
Father who is in Heaven. And I tell you, you are Peter, and on this
rock I will build My Church, and the powers of Hell shall 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 what you loose
on earth shall be loosed in Heaven' (Matthew 16:17-19). And after His
Resurrection, Jesus conferred upon Simon Peter alone the jurisdiction
of supreme shepherd and ruler over His whole fold with the words, `Feed
My lambs....Feed My sheep' (John 21:15-17) [...]

"(Canon) Therefore, if anyone says that the blessed Apostle Peter was
not constituted by Christ the Lord as the Prince of all the Apostles
and the visible head of the whole Church militant, or that he received
immediately and directly from Jesus Christ our Lord only a primacy of
honor and not a true and proper primacy of jurisdiction: let him be
condemned.

"Now, what Christ the Lord, Supreme Shepherd and watchful guardian of
the flock, established in the person of the blessed Apostle Peter for
the perpetual safety and everlasting good of the Church must, by the
will of the same, endure without interruption in the Church which was
founded on the rock and which will remain firm until the end of the
world. Indeed, `no one doubts, in fact it is obvious to all ages, that
the holy and most blessed Peter, Prince and head of the Apostles, the
pillar of faith, and the foundation of the Catholic Church, received
the keys of the kingdom from our Lord Jesus Christ, the Savior and the
Redeemer of the human race; and even to this time and forever he
lives,' and governs, `and exercises judgment in his successors' (cf.
Council of Ephesus), the bishops of the holy Roman See, which he
established and consecrated with his blood. Therefore, whoever
succeeds Peter in this Chair holds Peter's primacy over the whole
Church according to the plan of Christ Himself [...]. For this reason,
`because of its greater sovereignty,' it was always `necessary for
every church, that is, the faithful who are everywhere, to be in
agreement' with the same Roman Church [...]

"(Canon) Therefore, if anyone says that it is not according to the
institution of Christ our Lord himself, that is, by divine law, that
St Peter has perpetual successors in the primacy over the whole Church;
or if anyone says that the Roman Pontiff is not the successor of St
Peter in the same primacy: let him be condemned.

"We think it extremely necessary to assert solemnly the prerogative
which the only-begotten Son of God deigned to join to the highest
pastoral office. "And so, faithfully keeping to the tradition received
from the beginning of the Christian faith, for the glory of God our
Savior, for the exaltation of the Catholic religion, and for the
salvation of Christian peoples, We, with the approval of the sacred
council, teach and define that it is a divinely revealed dogma: that
the Roman Pontiff, when he speaks "ex cathedra", that is, when, acting
in the office of shepherd and teacher of all Christians, he defines, by
virtue of his supreme apostolic authority, doctrine concerning faith or
morals to be held by the universal Church, possesses through the divine
assistance promised to him in the person of St. Peter, the
infallibility with which the divine Redeemer willed His Church to be
endowed in defining doctrine concerning faith or morals; and that such
definitions of the Roman Pontiff are therefore irreformable because of
their nature, but not because of the agreement of the Church.

"(Canon) But if anyone presumes to contradict this our definition (God
forbid him to do so): let him be condemned" (Vatican I, "Pastor
Aeternus", Chaps. 1, 2 and 4).

Source: "The Navarre Bible: Text and Commentaries". Biblical text
taken from the Revised Standard Version and New Vulgate. Commentaries
made by members of the Faculty of Theology of the University of
Navarre, Spain. Published by Four Courts Press, Kill Lane, Blackrock,
Co. Dublin, Ireland.

Mass Readings

First reading	Acts 12:1 - 11 ©
It was about this time that King Herod started persecuting certain members of the Church. He beheaded James the brother of John, and when he saw that this pleased the Jews he decided to arrest Peter as well. This was during the days of Unleavened Bread, and he put Peter in prison, assigning four squads of four soldiers each to guard him in turns. Herod meant to try Peter in public after the end of Passover week. All the time Peter was under guard the Church prayed to God for him unremittingly. On the night before Herod was to try him, Peter was sleeping between two soldiers, fastened with double chains, while guards kept watch at the main entrance to the prison. Then suddenly the angel of the Lord stood there, and the cell was filled with light. He tapped Peter on the side and woke him. ‘Get up!’ he said ‘Hurry!’ – and the chains fell from his hands. The angel then said, ‘Put on your belt and sandals’. After he had done this, the angel next said, ‘Wrap your cloak round you and follow me’. Peter followed him, but had no idea that what the angel did was all happening in reality; he thought he was seeing a vision. They passed through two guard posts one after the other, and reached the iron gate leading to the city. This opened of its own accord; they went through it and had walked the whole length of one street when suddenly the angel left him. It was only then that Peter came to himself. ‘Now I know it is all true’ he said. The Lord really did send his angel and has saved me from Herod and from all that the Jewish people were so certain would happen to me.’

First reading

Acts 12:1 - 11 ©

It was about this time that King Herod started persecuting certain members of the Church. He beheaded James the brother of John, and when he saw that this pleased the Jews he decided to arrest Peter as well. This was during the days of Unleavened Bread, and he put Peter in prison, assigning four squads of four soldiers each to guard him in turns. Herod meant to try Peter in public after the end of Passover week. All the time Peter was under guard the Church prayed to God for him unremittingly.
On the night before Herod was to try him, Peter was sleeping between two soldiers, fastened with double chains, while guards kept watch at the main entrance to the prison. Then suddenly the angel of the Lord stood there, and the cell was filled with light. He tapped Peter on the side and woke him. ‘Get up!’ he said ‘Hurry!’ – and the chains fell from his hands. The angel then said, ‘Put on your belt and sandals’. After he had done this, the angel next said, ‘Wrap your cloak round you and follow me’. Peter followed him, but had no idea that what the angel did was all happening in reality; he thought he was seeing a vision. They passed through two guard posts one after the other, and reached the iron gate leading to the city. This opened of its own accord; they went through it and had walked the whole length of one street when suddenly the angel left him. It was only then that Peter came to himself. ‘Now I know it is all true’ he said. The Lord really did send his angel and has saved me from Herod and from all that the Jewish people were so certain would happen to me.’

Psalm or canticle: Psalm 33

Second reading	2 Timothy 4:6 - 18 ©
As for me, my life is already being poured away as a libation, and the time has come for me to be gone. I have fought the good fight to the end; I have run the race to the finish; I have kept the faith; all there is to come now is the crown of righteousness reserved for me, which the Lord, the righteous judge, will give to me on that Day; and not only to me but to all those who have longed for his Appearing. The Lord stood by me and gave me power, so that through me the whole message might be proclaimed for all the pagans to hear; and so I was rescued from the lion’s mouth. The Lord will rescue me from all evil attempts on me, and bring me safely to his heavenly kingdom. To him be glory for ever and ever. Amen.

Second reading

As for me, my life is already being poured away as a libation, and the time has come for me to be gone. I have fought the good fight to the end; I have run the race to the finish; I have kept the faith; all there is to come now is the crown of righteousness reserved for me, which the Lord, the righteous judge, will give to me on that Day; and not only to me but to all those who have longed for his Appearing.
The Lord stood by me and gave me power, so that through me the whole message might be proclaimed for all the pagans to hear; and so I was rescued from the lion’s mouth. The Lord will rescue me from all evil attempts on me, and bring me safely to his heavenly kingdom. To him be glory for ever and ever. Amen.

Gospel	Matthew 16:13 - 19 ©
When Jesus came to the region of Caesarea Philippi he put this question to his disciples, ‘Who do people say the Son of Man is?’ And they said, ‘Some say he is John the Baptist, some Elijah, and others Jeremiah or one of the prophets’. ‘But you,’ he said ‘who do you say I am?’ Then Simon Peter spoke up, ‘You are the Christ,’ he said ‘the Son of the living God’. Jesus replied, ‘Simon son of Jonah, you are a happy man! Because it was not flesh and blood that revealed this to you but my Father in heaven. So I now say to you: You are Peter and on this rock I will build my Church. And the gates of the underworld can never hold out against it. I will give you the keys of the kingdom of heaven: whatever you bind on earth shall be considered bound in heaven; whatever you loose on earth shall be considered loosed in heaven.’

Gospel

When Jesus came to the region of Caesarea Philippi he put this question to his disciples, ‘Who do people say the Son of Man is?’ And they said, ‘Some say he is John the Baptist, some Elijah, and others Jeremiah or one of the prophets’. ‘But you,’ he said ‘who do you say I am?’ Then Simon Peter spoke up, ‘You are the Christ,’ he said ‘the Son of the living God’. Jesus replied, ‘Simon son of Jonah, you are a happy man! Because it was not flesh and blood that revealed this to you but my Father in heaven. So I now say to you: You are Peter and on this rock I will build my Church. And the gates of the underworld can never hold out against it. I will give you the keys of the kingdom of heaven: whatever you bind on earth shall be considered bound in heaven; whatever you loose on earth shall be considered loosed in heaven.’