A challenge it is, to approach apparitions and other so-called phenomena with equipoise.
How to discern a real supernatural episode from a false one?
That's easier said than done.
The most valuable passage from the Bible may be the one that tells us to keep what is good and discard the rest (1 Thessalonians 5:21).
In other words, don't always toss out the baby with the bathwater. But do test that bathwater! It can be badly tainted.
Many real experiences are compromised by the time they get through the medium of the sensible faculties. Most (when they are not mere imagination) are a "mix."
The most frequently cited standards come from Scripture: "You will know them by their fruits" (Matthew 7:16) and "By this you know the Spirit of God: every spirit that confesses that Jesus Christ has come in the flesh is from God" (1 John 4:2).
The problem is that religious apparitions virtually always acknowledge Jesus (deceptive or not), and "fruits" aren't always initially apparent, or on the other hand are deceptively fleeting (good things are seen on the surface).
Discernment comes chiefly through fasting, receiving the Eucharist, Adoration (with a confessed heart), humility (critical), love, and prayer. There is no magic formula.
Some things are obvious: Be wary of a seer who is prideful, haughty, rude, attention-seeking, loquacious (locutions that are too long and wordy), sullen, insistent, or divisive. They claim more than they present evidence for, take more than they give.
The renowned mystical theologian Father Augustin Poulain, in his classic, The Graces of Interior Prayer, said:
"When a seer wishes to be believed on his bare word, we can generally get rid of him by saying: 'You assure me that God speaks by your mouth. I have no right to believe you unless you prove it. What sign do you bring?' In his ingenuousness he had not expected this question, and retires abashed."
Beware, said Poulain, of a seer who tells you that Heaven has mentioned or chosen you (as a spiritual director, in the case of a priest).
When a seer has had prophecies that did not materialize, this is most certainly a warning signal. The person who mouths a false prediction or posits dates is what Scripture calls "presumptuous." Nor are we to become overly attracted and attached to alleged mystics (and hostile to those who differ). Fanaticism, cult, and rancor are bad fruits for certain (as opposed to heartsease, patience, and joy).
Imagination? "When people strongly desire a thing, the imagination makes them fancy they see or hear it, just as when one's mind is set on a subject all day, one dreams of it at night," said Teresa of Avila. The evil, she says, is not usually in the vision so much as in the person.
At the same time (here comes that balance again -- or is it a tightrope?): there are those too disposed toward skepticism and even caustic disregard due to a mechanistic mindset nurtured strongly by the current educational culture.
If we are humble, said Saint Teresa, a vision, whatever the source, will do us no harm. "The good or the evil is not in the vision," she said, "but in him to whom it is given, and who does not profit by it in humility."
"If we believe a corporeal apparition of Our Lord or of the saints to be due to the devil," is one of Poulain's rules, "[do] not to go to the length of insulting it or treating it with contempt, any more than we should do towards a sacred picture that had been painted by a scoundrel."
The Venerable Louis du Pont related the account of a priest who received visions. One day, he asked himself if he was not the sport, notes Poulain, of his own imagination. "He then heard Our Savior address these words to him: 'When thou art hungry, if thou art given a branch of a tree loaded with fruit, what dost thou do?' 'I eat the fruit and cast the branch away,' he replied. 'Even so,' Our Savior continued, 'act in the same way with regard to the visions. Eat the fruits thereof, humility, patience, and the other virtues; and whatever the vision may be, be not troubled any more.'"
Sounds like good advice to us. We must be cautious. Discern always. But first make certain you have discerned yourself.
[resources: The Last Secret -- apparitions since the first century]