St. Francis de Sales on Miracles as Proof of the True Church
"The Church then has milk and honey under her tongue and in her heart, which is interior sanctity, and which we cannot see: she is richly dressed with a fair robe, beautifully bordered with varieties, which are her exterior sanctities, which can be seen. But because the sects and heresies disguise their clothing, and by false stuffs make them look like hers, she has, besides that, perfumes and odours which are her own, and these are certain signs and shinings of her sanctity, which are so peculiarly hers, that no other society can boast of having them, particularly in our age.
For, first, she shines in miracles, which are a most sweet odour and perfume, and are express signs of the presence of the immortal God with her, as S. Augustine styles them. And, indeed, when Our Lord quitted this world he promised that the Church should be filled with miracles: These signs, he said, shall follow them that believe: in my name- they shall cast out devils, they shall speak with new tongues they shall take up serpents, poison shall not hurt them, and by the imposition of hands they shall heal the sick. (Mark ult.).
Besides, I beg you to show me at what period the visible Church may have been without miracles, from the time that it began until this present? In the time of the Apostles there were miracles beyond number; you know that well. After that time, who knows not the miracles, related by Marcus Aurelius Antoninus, worked by the prayers of the legion of Christian soldiers who were in his army, which on this account was called thundering? Who knows not the miracles of S. Gregory Thaumaturgus, S. Martin, S. Anthony, S. Nicholas, S. Hilarion, and the wonders concerning Theodosius and Constantine, for which we have authors of irreproachable authority - Eusebius, Rufinus, S. Jerome, Basil, Sulpicius, Athanasius? Who knows not again what happened at the Invention of the Holy Cross, and in the time of Julian the Apostate? In the time of SS. Chrysostom, Ambrose, Augustine, many miracles were seen, which they themselves relate why then would you have the same Church now cease from miracles? What reason would there be? In truth, what we have always seen, in all varieties of times, accompanying the Church, we cannot do otherwise than call a property of the Church.
The true Church then makes her sanctity appear by miracles. And if God made so admirable the Propitiatory, and his Sinai, and his Burning Bush, because he wished to speak with men, why shall he not have made miraculous this his Church in which he wills to dwell for ever?"