The reading of the day is from from Matthew 16:13-19:

When Jesus went into the region of Caesarea Philippi he asked his disciples, "Who do people say that the Son of Man is?" They replied, "Some say John the Baptist, others Elijah, still others Jeremiah or one of the prophets." He said to them, "But who do you say that I am?" Simon Peter said in reply,  "You are the Christ, the Son of the living God." Jesus said to him in reply, "Blessed are you, Simon son of Jonah. For flesh and blood has not revealed this to you, but my heavenly Father. And so I say to you, you are Peter, and upon this rock I will build my Church, and the gates of the netherworld shall not prevail against it. I will give you the keys to the Kingdom of heaven. Whatever you bind on earth shall be bound in heaven; and whatever you loose on earth shall be loosed in heaven."

Now the refection titled,  "The Grace of the Chair of Peter."

At the center of all Catholic doctrine, liturgy, morality, and prayer is the person of Jesus…. He has reconciled us with the Father, establishing peace through the blood of his cross (Col 1:20)…. Salvation and sonship—these are what Jesus won for us. Yet these gifts must still be ­extended throughout the world and throughout history. He ­desires that every soul encounter him, that he be formed in ­every soul…. When Jesus ascended into heaven, he did not leave behind a book, or even instructions to write a book. Rather, he left behind a hierarchical community of believers, his Church. And he established this not as a merely human organization but as his abiding presence in the world—as his Body animated by his Spirit….

To accomplish her mission of forming Christ in souls, the Church must possess the means to do so. And so she does, most notably the authority to teach Christ’s truth and communicate his grace. The Church teaches authoritatively what to believe (doctrine) and how to live (morals). This authority, so often seen as a threat to human freedom, in fact answers the longings of the human heart. We all want to know what is true and to do what is right. Uncertainty, not a teaching authority, is the enemy of human freedom. As long as we are uncertain, we will not give ourselves generously. We remain enslaved in doubt. Confidence in the truth about Jesus and his narrow path frees us to run that path joyfully. The Church teaches authoritatively the truth that sets us free. But to know the truth is not enough. Since we remain weak and ignorant, we need Christ’s grace to strengthen and enlighten us. Thus the Church administers the sacraments to her members, to bring them divine life, to nourish them, and to heal them when necessary…. These means of grace, entrusted to the Church for the salvation of souls, have as their ­ultimate purpose the formation of Christ within us.

Who do you say that I am? Jesus put this question to his apostles, and it echoes throughout history. It is, in the end, the only question that matters. The Catholic Church exists, ultimately, as a living response to that question and to form the response in every soul: You are the Christ, the Son of the living God.