Jesus 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.” 
(Mt 16:13-19)

The liturgy is sometimes very funny. We celebrate the birthdays of churches, we can even celebrate the birthdays of chairs! Today, of course, is the feast of a very important chair, the chair of Saint Peter. And we celebrate our union in faith with the successor of Saint Peter, who sits on that chair today, Pope Francis.