Where did Jesus utter those words to Peter, announcing the creation of the Church to come?
The answer is "Caeserea Phillipi", located in northern Israel near the Hermon and Jordan Rivers. At that spont, an imposing rock cliff rises 100 feet off the ground, with a warren of caves at its base and water flowing out.
Herod the Great dedicated a temple to Augustus at this site, but more importantly, prior to this it was a temple dedicated to the Greek God of Pan. Pan was the god of "desolate places", and so, Caeseara Phillipi was popularly nicknamed "the gates of Hell".
It's no coincidence that Jesus gave Peter (the Rock) the keys to the kingdom of heaven at the site of "the rock" which was the domain of the mythological Pan. The Church that Christ announced would usurp the dominion of Roman idolatry and the cult of the Gentile demon, "Pan", and from this rock would flow life-giving water instead. "...and the gates of hell shall not prevail against it." (Mt 16:18)
"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.”
(Matthew 16:18-19)
You are probably aware of the phrase, "the infallibility of the Pope". It's a provocative statement, indeed! However, papal infallibility (formally defined at the First Vatican Council) is much less imposing than the words suggest.
...We teach and define that it is a dogma Divinely revealed that the Roman pontiff when he speaks ex cathedra, that is when in discharge of the office of pastor and doctor of all Christians, by virtue of his supreme Apostolic authority, he defines a doctrine regarding faith or morals to be held by the universal Church, by the Divine assistance promised to him in Blessed Peter, is possessed of that infallibility with which the Divine Redeemer willed that his Church should be endowed in defining doctrine regarding faith or morals, and that therefore such definitions of the Roman pontiff are of themselves, and not from the consent of the Church, irreformable.
--First Vatican Council, 1870
By the parameters of this definition, the Pope has only formally exercised the charism of infalliblity on two occasions: declaring the dogma of the Assumption (1950), and declaring the dogma of the Immaculate Conception (1854).
That's not to say the pope never speaks infallibly on other occasions. For example, anytime he reiterates the universal doctrine of the Church, he speaks infallibly, because Catholic doctrine, itself, is infallible. But there is a very fine line between an infallible statement, and the private opinion of this pope or that. Pope Benedict XVI, for example, wrote a trilogy of books on Our Lord during his pontificate, but at the outset, he was careful to add the disclaimer that he was speaking only as a private theologian, not as "the pope".
Pope Francis enjoys giving interviews, many of which are off-the-cuff, but contain provocative ideas. These situations of theological speculation and personal opinon are not exercises of infallibility, yet we are obliged to give due respect and consideration, regardless. For two millenia, the Church has populated the arena of ideas as a step in discerning the voice of the Holy Spirit. In the end, it is not the opinion of a pope, but the will of the Holy Spirit that results in a particular teaching or tradition to take on the quality of infallible Truth. The Assumption of Mary, declared dogma in 1950, for example, was speculated on and feted by the Church going all the way back to the 4th century! It was not a "new" teaching. It was only formally defined in order to cast aside all doubts of its Truth and to highlight its place in Divine Revelation.