Private Revelation vs. Public Revelation
God revealed Himself to humanity in a universal way through public revelation. This self-revelation was made perfectly in Jesus Christ, God made man. The deeds and words of Almighty God in the Old and New Testaments, culminating in Jesus, show us who God is, His great love for us, and everything that we need to be saved.
On the other hand, private revelation does not have this universal character, nor is it necessary for salvation. God has allowed private revelation to help the believer in his or her belief. These apparitions of saints and the Blessed Mother, and other miraculous events and messages, do not demand faith from the People of God. They do not add to the Deposit of Faith which is comprised of the Revelation of the Word of God. The Word of God is Jesus Christ Himself communicated to us through the Church as Sacred Scripture, Sacred Tradition, and interpreted by the Magisterium.
Private revelation, according to the Catechism of the Catholic Church, is there to help the faithful “live more fully by [Christ’s definitive Revelation] in a certain period of history (CCC 67).” So, private revelation never adds anything new to the Faith; it can simply serve as a reminder.
Effect of Mass Media
Today, we live in an age of unprecedented connectivity in terms of the sharing of information. In the past, there was time for the Church to respond to alleged miracles and apparitions with prudence and careful examination. Now, because of the mass media, an alleged visionary can share their message in seconds. Even before the dawn of the internet, the Congregation for the Doctrine of the Faith (CDF) clarified what was required in examining private revelation to better answer this modern challenge.