C.S. Lewis wrote in his preface to The Screwtape Letters that there are two similar although complementary pitfalls into which one can fall when it comes to devils: either doubting their very existence or believing in them, but with an excessive interest - almost an obsession. The devils themselves delight in both and welcome a materialist as wholeheartedly as they do a magician. Their technique consists in convincing someone to be one or the other and then separating him from everyone else forever. Is it not true that the arts of the materialist and of the magician are back in fashion? Thus the devil's existence is denied by portraying him as a mere symbol of evil, or else, by attributing all man's misfortunes to him - including those of the Church - to the point of clouding the responsibility of men and of pastors. As St Augustine brilliantly said in one of his discourses (163B): "The devil must not be blamed in every instance; sometimes, in fact, man himself is a devil towards himself. So why must we beware of the devil? Precisely for this reason: so as not to deceive ourselves." Nonetheless, one thing prompted me to pay close attention to this correspondence and to ensure that it was not lost. Above all, the devil and the priest do the same job: they go in search of souls. And both of them could, without difficulty, make their own the motto of St John Bosco: Da mihi animas, cetera tolle - "Give me souls and take away all the rest". And so the time has come to take a look at this correspondence and to get to know that ancient craft, of which the practitioners have a predilection for the soul above all else: the soul, the real man as he is himself, who will be forever himself and cannot be confused with anyone else. One last word to the wise reader. The names chosen do not correspond to any particular person. They are rather the free expression of a way of thinking which, by some strange coincidence, brings the world of mortals closer to that of the hereafter.