How can one tell the difference between mental illness and possession? " If something that seems extraordinary is a mental illness, it will get progressively worse and obvious psychosis will develop." Schizophrenia can be distinguished from possession because there are no extraordinary phenomena in schizophrenia. Can demons read our thoughts? No. Can they cause natural disasters? No, unless we have strong evidence to the contrary. Can the devil have a human child? No, because the devil is a spirit. Why do some exorcism last so long? Because there are some demons whose angelic nature belonged to a higher order.
Fr Fortea does not have the answer to all the questions. For example, why do demons use the bodily senses to possess someone? He admits his answer is speculative.
There are some wonderful answers. What is more important, confession or exorcism? Confession, because exorcism only drives out a demon from one's body. Confession drives out evil from one's soul.
We are in the hands of a master. A wonderful work.