This series is about belief. It is about the belief in the truths contained in the Apostles Creed and all that the Church includes in what is known as the Deposit of Faith. In other words, it is not about what is found in an encyclopedia or in a similar comprehensive statement of human knowledge.
The new Catechism tells us that “God graciously arranged that the things he had once revealed for the salvation of all peoples should remain in their entirety, throughout the ages, and be transmitted to all generations.” (74).  That body of knowledge is what is known as the Deposit of Faith. And nothing can be added to it which closed with the death of the last Apostle.
Thus, what we believe is safeguarded by the Church for all time and will remain intact as what God wanted revealed to us. There is nothing that needs to be known about God that has not already been revealed by God. In other words, there can be no innovations or truths yet to be known that are not already in the deposit of faith. However, “Yet if Revelation is already complete, it has not been made completely explicit; it remains for Christian faith gradually to grasp its full significance over the course of the centuries.”(66).
Of course, making something more explicit is not the same as introducing something entirely new.
The deposit of faith is also known as “public revelation” to distinguish it from “private revelation”.
The main difference between public and private revelation is that everything that is contained in public revelation has to be believed. There can be no picking and choosing of individual truths to suit onès own self.or preference. Even if a private revelation is recognized by the Church as authentic and genuinely from God, it does not have to be accepted for belief as do the truths contained in the public revelations.
What then is the purpose of private revelation? The new Catechism informs us that “private revelations can help us to live more fully our Christian faith in a certain period of history.” (67).
We should be most grateful to God for providing us with an unchangeable body of truth that cannot be changed to suit the notion of anbody at any time.
The numbers in brackets refer to sections in The Catholic Catechism.