There is a text that has become standard for the study of religious experience and phenomena by Rudolph Otto entitled The Idea of the Holy.
In this book, Otto uses the phrase tremendum et fascinans (roughly translated as “fear and fascination”) to indicate what it means to encounter sacred realities. The sacred, be it a place, person, or thing, can evoke the frightening but still remain attractive and compelling. The holy is terrifying, yet at the same time, irresistible.
I have always found Padre Pio to be a kind of embodiment of Otto’s principle. The Church celebrates Saint Pio of Pietrelcina today, September 23.