It is hardly necessary to observe that Catholics are warned to be most careful not to suffer themselves to be the victims of hallucination or fraud — a warning which is of far greater importance in the case of any vision (for example, of our Lord or the Blessed Virgin) which purports to be of public interest, and to convey a message to the world, than it can be when a friend appears, so to speak privately, from the other world to his friend, merely for his consolation or to ask prayers for the repose of his own soul.
Wherever there is question of any apparition that purports to bring a message from Heaven, the Church is accustomed to step in with her well-known caution, often imposing strict regulations of silence upon all concerned until the alleged events have been juridically and thoroughly investigated.
The truth of every vision depends ultimately upon the strength of the evidence, by which it is proved to be real and to have come from God. Still, I think that a Catholic would be rash indeed were he (with out the strongest reasons, could such be imagined to exist) to deny the reality of such visions, as those of our Lord to St. Juliana, and to St. Margaret Mary Alacoque (which resulted in the institution of the Feasts of Corpus Christi and the Sacred Heart), or of the Blessed Virgin at Lourdes—since upon such visions as these (I think that there are but few) the Church would seem to have set definitely, and even authoritatively, the seal of her sanction and approval.
The principles that apply to visions hold also with respect to miracles. On the one hand much care should be exercised before we accept the miraculous character of any extraordinary event; on the other hand it may not be asserted by Catholics that miracles have altogether ceased in the Church from the days of the Apostles to our own, nor may it lawfully be denied that they will continue to the end. For those at least who believe in the Bible, the words of Cardinal Newman should settle the matter, so far as reasonableness is concerned. " Protestants assert that since miracles once occurred they are likely to have ceased ; Catholics maintain that the fact that they took place once constitutes a presumption of their continuance." No doubt miracles were more numerous in the early centuries, in times when they were still necessary for the confirmation of the Faith, than has been the case in succeeding ages. Nevertheless, the evidence that they have taken place in every century and all over the world is overwhelming when it is examined dispassionately and apart from the prejudice which, on a priori grounds, denies the possibility of the miraculous, and consequently refuses to look seriously at the facts.
In this book I am concerned solely with visions and miracles of our Lady. The miracles worked by our Lady are innumerable. We have accounts of apparitions of our Lady recorded without interruption throughout the course of Christian history, and though they may be separated by long tracts of time, they singularly resemble one another in their external characteristics. All that I can do here is to narrate the leading facts concerning a few of these wondrous events, and leave them to speak for the rest. As I must make some choice, I will take three visions of our Lady, which are connected with the names of the great Gregories in the early centuries, and then will pass abruptly to the nineteenth century in France.