The song is based on a passage in the 1969 book God and the Soul by Peter Geach:
In a Muslim story, a fallen champion saw a Crusader wielding against him a magic invincible sword bearing the name of God: ‘Sword’ he cried ‘can you strike a true believer? Do you not know the name on your blade?’ 'I know nothing but to strike straight', the sword replied. 'Strike then, in the name of God!' Logic is not partisan, and knows nothing but to strike straight; but the sword is invincible, bearing the Maker’s name.