[T]he word of God is so far off from finding fault with war begun upon a just quarrel, that it doth both make laws of war, and sheweth a number of examples of upright wars, of wise and worthy warriors. The laws of war are recited in the 20th chapter of Deuteronomy, both profitable and necessary, and therewithal so evident, that they need no words of mine to expound them. Moreover, in every place of the scripture these laws of war are still bidden to be kept.
First of all, the chief and uppermost place must be given to religion in every camp and garrison: for the Lord himself hath appointed priests and ministers of true religion to attend and serve in wars.
Secondarily, let upright laws be of force in camps abroad, as well as in cities at home: let soldiers live honestly, justly, and rightly, as order and discipline are wont to require when as they are in the city at home. For that saying cometh not of God, but of the devil, which is commonly spread abroad, Let laws in war be hushed and still.
Thirdly, let him that is chosen to be guide and general of the war be godly, just, holy, valiant, wise, and fortunate; as, among them of old, were Josue, David, Judas Machabeus, Constantine, Theodosius, and many more. To all this there must be added a chosen band of tried men: for choice of soldiers must be made, unless perhaps the army do consist in a troop of bastards and unskilful men, of perjured and blaspheming knaves, of cut-throats and rakehells, of drunkards and gluttons, and a beastly drove of filthy swine. Victory consisteth not in the multitude of men, but in the grace of God and a chosen band. The proverb is common which saith, “Where a multitude is, there is confusion.” Great and innumerable armies are a let to themselves very greatly; as we do learn by daily experience, and as examples of every age do testify to us. Moreover, loiterers in camps are always reproved. Let the christian soldier, therefore, be idle at no time; let him ever be busy, and still doing something: let him be courageous, faithful to his country, ready to take pains, obedient to his captains, fit to take time when occasion is offered, and evermore occupied in warlike discipline; no effeminate milksop, but of manly stomach; not cruel and merciless, but severe and pitiful, as time requireth. What he may preserve, that let him not destroy.
But, above all things, let him not forget or think scorn, both in peril and out of peril, evermore to make his prayers and supplications to God his Saviour. In God's name let him begin all things; without God let him attempt nothing: in adversity, and when he hath the overthrow, let not his courage quail, nor his heart and hope forsake him; in prosperity let him not be puffed up with pride and arrogancy, but let him give thanks to God, and use the conquest like a merciful victor: let him wholly depend upon God's helping hand, and desire nothing rather than the defence of the commonweal, laws, religion, justice, and guiltless people.
Heinrich Bullinger, The Decades of Henry Bullinger: The First and Second Decades, ed. Thomas Harding (The University Press, 1849), 380, 381.