The Third Secret is a prophecy. We know that from Cardinal Ottaviani who read it and said so, and from Cardinal Ratzinger who said in the 1984 interview that if the Secret was not published at least for now it was to “avoid confusing religious prophecy with sensationalism.” It is a prophecy that began to be realized at least by 1960, which Sister Lucy said was the year by which the prophecy of the Third Secret will be “much clearer.” It is a prophecy that tells us about our time. It is a loving warning from Our Lady and also advice on how to act in these circumstances.
We are told by the Third Secret of Our Lady of Fatima that the dogma of Faith will be preserved in Portugal, and this is clearly understood by all the Fatima experts to mean that the dogma of Faith will not be preserved elsewhere. That is the first essential point of the Third Secret.
Therefore, the Third Secret concerns, first of all, the dangers to the Faith, just as Cardinal Ratzinger said in 1984. St. John tells us what it is that overcomes the world: he says it is our faith. For the world to overcome the Church, it has to overcome our faith first of all. And so that is what the Secret concerns: our faith. We know this from Our Lady’s words given to us by Sister Lucy in 
the beginning of the Third Secret; we know it from Cardinal Ratzinger; we know it from the Bishop of Fatima; we know it from the remarks of the Pope at Fatima in 1982 and 2000. It concerns our faith. There is no question about that.
Secondly, it concerns the dogma of the Faith. Our Lady of Fatima spoke about the dogma of the Faith as always being preserved in Portugal. Why did Our Lady speak about the dogma of the Faith? She spoke about dogma because that would be the target of those who would attack the Church from within. What is dogma? Dogma is what has been infallibly defined. The dogma of the Faith is known by the solemn, infallible definitions of the Magisterium of the Church. The word infallible means “cannot fail”. Therefore, the definitions of the Faith, solemnly defined by the Church, cannot fail. So we know what the Faith is, what the dogma of the Faith is, by the infallible definitions.
The problem is that since Vatican II we have new notions being passed off in the Church as “new” Catholic doctrine which appear to contradict or at least “revise” the infallible definitions. But as Vatican I clearly taught, the infallible Magisterium — which means the Pope definitively teaching the universal Church either alone or together with all the bishops — cannot give us new doctrine. The Magisterium can only pass on and fully explain what God revealed through the apostles. There is no new doctrine being revealed by God since the death of the last Apostle, Saint John. So this “new” doctrine is really pseudo-doctrine. This pseudo-doctrine is being taught very subtly; but when it contradicts the doctrine which has been infallibly defined, then we have to believe the infallible doctrine and we must reject the “new” doctrine. And so, it’s important for us to realize that it is the dogma of the Faith that cannot fail. Men can fail; lay people can fail; priests can fail; bishops can fail; cardinals can fail; and even the Pope can fail in matters which do not involve his charism of infallibility, as history has shown us with more than one pope (e.g. after Pope Honorius died, he was condemned by the Third Council of Constantinople [680 A.D.] for aiding and abetting heresy, and that condemnation was approved by Pope Leo II and repeated by later popes). But the solemn definitions of the Faith by the Pope, or the Pope together with all the bishops in a Council of the Church, cannot fail.
Everything should be judged by those definitions that cannot fail. And so if a pope, a cardinal, a bishop, a priest, or a layman teaches us something contrary to any definition of the Faith, we can know that that layman, priest, bishop, cardinal, or pope is wrong. For example, when John XXII, back in the 14th Century, gave sermons (but not solemn definitions) in which he insisted that the blessed departed do not enjoy the Beatific Vision until the day of General Judgment, he was denounced and corrected by theologians, and he finally retracted his heretical opinion on his deathbed.
And how can we be so sure? Because the definition is infallible, it cannot fail. As I said – a pope, a cardinal, a bishop, a priest and a layman can fail. Yes, even the Pope can fail, and he does fail if he expresses an opinion which is contrary to a solemn, infallible definition of the Catholic Church. This does not mean the Church fails when this happens, but only that the Pope has made a mistake without imposing it on the whole Church. As we see with the example of John XXII, the Pope can make a mistake in some teaching or opinion which has not been imposed upon the Church with a solemn, infallible definition. And so when Our Lady speaks about the “dogma of the Faith”, She indicates to us that the danger to the Faith is clearly seen when the solemn dogmatic definitions of the Catholic Faith are contradicted. The definitions themselves cannot fail.
Reality Meets Faith 