The argument of this book is simply that, contrary to what is widely assumed, the clergy in western Christianity (at least in the Roman Catholic and Anglican-Episcopal traditions) have not been categorically forbidden to bear arms since the High Middle Ages (c.1100–1300) and are not today. Readers intrigued enough to go on, but still concerned about the efficient use of their time, are advised to proceed directly to the Conclusion after finishing this Introduction. They are warned, however, that most of the juicy bits lie in between.

Even historians who have worked on some aspect of this subject habitually either assume that clerics who bear arms automatically violate canon or ecclesiastical law, or else they considerably oversimplify the matter. In his Christian Attitudes Toward War and Peace Roland Bainton wrote that ‘The approval of the Church was never bestowed on those clerics and monastics who had taken defense into their own hands. St Thomas, writing even after the commencement of the crusades, held that the clergy should be excluded from military functions, not so much, however, for ethical as for sacramental reasons.’ As we shall see, Bainton has, like so many others, confused Aquinas' opinions as a theologian with the law of the church.

A definitive reference work, The Oxford Dictionary of the Christian Church, asserts in an entry on ‘war, participation of the clergy in’, that ‘Since the Middle Ages clerics in major orders have been expressly forbidden to take a direct part in the shedding of blood.’