Garrigou-Lagrange helps us understand private revelations. Here is the first of a few quotations on separate posts.
The second post is on visions. I hope people can discern the distinctions here.
... we must distinguish two kinds of private revelations: (I) revelations properly so called reveal secrets about God or His works; (2) revelations improperly so called give a greater understanding of supernatural truths already known by faith.(27)
I) Revelations manifesting secrets to us are much more subject to illusion. Without doubt God sometimes reveals to the living the time that remains to them on this earth, the trials that they will undergo, what will happen to a nation, to a certain person. But the devil can easily counterfeit these things and, to gain credence for his lies, he begins by nourishing the spirit with likely things or even with partial truths.(28) St. John of the Cross says: "It is almost impossible to escape his wiles if the soul does not immediately get rid of them, because the spirit of evil knows well how to assume the appearance of truth and give this appearance credit." (29) "In order to be perfect there is, therefore, no reason to desire these extraordinary supernatural things. . . . The soul must prudently guard itself against all these communications if it wishes, in purity and without illusions, to reach divine union by the night of faith." (30) No words could make a clearer distinction between these extraordinary supernatural things and infused contemplation, and more effectively show that infused contemplation is normal in the perfect.
2) Revelations improperly so called, which give us a greater understanding of revealed truths, are associated with infused contemplation, especially if they concern God Himself and do not stop at particular things, but profoundly penetrate His wisdom, infinite goodness, or omnipotence. In The Ascent of Mount Carmel St. John of the Cross says on this subject: "This profound loving knowledge is, moreover, accessible only to a soul in union with God. Such knowledge is this union itself, for it has its origin precisely in a certain contact of the soul with the Divinity. Consequently it is God Himself who is felt and tasted, though He is not perceived manifestly in full light, as He is in glory; but the touch is so strong and so profound, by reason of the knowledge and attraction, that it penetrates the substance of the soul. It is impossible for the devil to interfere in this and to deceive by imitation, for nothing is comparable to it, or approaches it in enjoyment and delights. These touches savor of the divine essence and of eternal life, and the devil cannot counterfeit such lofty things. . . . In regard to the other perceptions, we said that the soul should abstract itself from them, but this duty ceases in the case of this lofty loving knowledge, since it is the manifestation of that union to which we are trying to conduct the soul. All that we have taught previously on the subject of despoliation and of complete detachment was directed toward this union; and the divine favors which result from it are the fruit of humility, of the desire to suffer for the love of God, with resignation and disinterestedness as to all reward." (31)