In The Varieties of Religious Experience (1902), psychologist William James wrote:
It is true that we instinctively recoil from seeing an object to which our emotions and affections are committed handled by the intellect as any other object is handled. The first thing the intellect does with an object is to class it along with something else. But any object that is infinitely important to us and awakens our devotion feels to us also as if it must be sui generis and unique. Probably a crab would be filled with a sense of personal outrage if it could hear us class it without ado or apology as a crustacean, and thus dispose of it. “I am no such thing,” it would say; “I am MYSELF, MYSELF alone.
James is saying that we resist pointing the intellect at matters of the heart, or in this case the spirit. He goes on to say that although this reaction is normal, it’s unnecessary. We can separate the “existential” analysis (what is the thing, where does it come from, how does it behave) from the “value” analysis (is it good or bad). In the end, the value analysis for mental states is intuitive. We can tell the good states from the bad. We don’t need to prove it with science. But in his time, people twisted themselves in knots trying to find anatomical or otherwise deterministic support for arguments that were, at bottom, value-judgments. And people still do this today.

More from James:
Medical materialism seems indeed a good appellation for the too simpleminded system of thought which we are considering. Medical materialism finishes up Saint Paul by calling his vision on the road to Damascus a discharging lesion of the occipital cortex, he being an epileptic. It snuffs out Saint Teresa as an hysteric, Saint Francis of Assisi as an hereditary degenerate. George Fox’s discontent with the shams of his age, and his pining for spiritual veracity, it treats as a symptom of a disordered colon. Carlyle’s organ-tones of misery it accounts for by a gastro-duodenal catarrh. All such mental overtensions, it says, are, when you come to the bottom of the matter, mere affairs of diathesis (auto-intoxications most probably), due to the perverted action of various glands which physiology will yet discover. And medical materialism then thinks that the spiritual authority of all such personages is successfully undermined.
In short, the most moving, inspiring, devout, holy people in history—people he calls “religious geniuses”—likely all would have been diagnosed with a mental disorder today. And their suffering was real. But the results of their feelings, the impact of the world, and our judgments of their value, are not pathological.