Compendium, 1, 1, 2: "God Comes to Meet Man" (10)

10. What is the value of private revelations?

(Catechism 67)
While not belonging to the deposit of faith, private revelations may help a person to live the faith as long as they lead us to Christ. The Magisterium of the Church, which has the duty of evaluating such private revelations, cannot accept those which claim to surpass or correct that definitive Revelation which is Christ.

Private revelation is spoken about from time to time in the Catholic Church - some of it works its way into our liturgy, even, as in the case of St Faustina's vision of Christ's Divine Mercy. But, and this is an important understanding, her vision of Christ's Divine Mercy is able to be incorporated into the liturgy because it is an affirmation of the deposit of faith handed down by the apostles - no one questions the great mercy of Christ. That being said, private revelation, even when given the seal of authenticity after an ecclesial inquiry does not change or add to the deposit of faith. The Church does not have the authority to do so. So though many may pilgrimage to Lourdes to visit the grotto there, and though the Church has authenticated that Marian apparition, the vision does not change the teaching of the Church, but is seen as a help for today - is seen as private. (I might add here that if the vision contravened the deposit of the faith it could not be authenticated by the Magisterium of the Church.)

Most Christians would not question the possibility of private revelation, though I know a few who would. The possibility of private revelation is borne out in smaller ways in our own lives - in little epiphanies that we have as we read the Scriptures, or in the stranger in the grocery store who says the very thing we need to hear the moment we need to hear it, or in the audible voice we hear answer the prayer of our heart. These small illuminations meet a moment, they give hope and encouragement. And we move forward.