Diabolical possession is the devil’s hideous parody of the union between Christ and the soul in the spiritual marriage. Whereas the marriage of Christ with the soul is the consummation and seal of a union by grace long adorned with the constant display of acts of heroic virtue, the diabolical counterfeit is achieved usually after the subject’s long-continued and progressive indulgence in vice. The comparison is introduced only to indicate the nature of possession. Nor is it exact, for whereas Christ can possess only the souls of the good, it would seem that diabolical possession can sometimes occur when there is no deep-rooted habit of sin, and even in persons noted for holiness of life.

It is possible, however, that many records of supposed diabolical possession have not distinguished properly between ‘possession’ and ‘obsession’. In possession proper the grasp of the devil acts as a directive force; he can influence conduct. Nevertheless, the connection between man and his diabolical control is not strictly as between slave and master; it is more a partnership, in which the devil has the controlling interest. The man does not cease to be a man, nor to behave as a man. People may rave and blaspheme under diabolic influence; but they may also behave quite ‘properly’. They act always the part that suits the enemy of souls for the time being.

Obsession, on the other hand, is an incomplete and less disastrous form of diabolical influence. It operates chiefly through the imagination, and its effect is to worry or torture the mind, with less direct compelling force than in the possessed soul.