Mark 16:18

That is, they shall scatter before them serpents, whether intellectual or sensible, as it is said, Ye shall tread upon serpents and scorpions, which is understood spiritually. But it may also mean sensible serpents, as when Paul received no hurt from the viper. There follows: And if they drink any deadly thing, it shall not hurt them. (Luke 10:19) We read of many such cases in history, for many persons have drank poison unhurt, by guarding themselves with the sign of Christ. It goes on: They shall lay hands on the sick, and they shall recorer.

(ubi sup.) Are we then without faith because we cannot do these signs? Nay, but these things were necessary in the beginning of the Church, for the faith of believers was to be nourished by miracles, that it might increase. Thus we also, when we plant groves, pour water upon them, until we see that they have grown strong in the earth; but when once they have firmly fixed their roots, we leave off irrigating them. These signs and miracles have other things which we ought to consider more minutely. For Holy Church does every day in spirit what then the Apostles did in body; for when her Priests by the grace of exorcism lay their hands on believers, and forbid the evil spirits to dwell in their minds, what do they, but cast out devils? And the faithful who have left earthly words, and whose tongues sound forth the Holy Mysteries, speak a new language; they who by their good warnings take away evil from the hearts of others, take up serpents; and when they are hearing words of pestilent persuasion, without being at all drawn aside to evil doing, they drink a deadly thing, but it will never hurt them; whenever they see their neighbours growing weak in good works, and by their good example strengthen their life, they lay their hands on the sick, that they may recover. And all these miracles are greater in proportion as they are spiritual, and by them souls and not bodies are raised.