The Ecumenical Councils of Trent and Vatican I and the Creed of Pius IV all require us to:
…accept the Holy Scripture according to that sense which holy mother the Church hath held, and doth hold, and to whom it belongeth to judge the true sense and interpretations of the Scriptures [and] never take and interpret them otherwise than according to the unanimous consent of the Fathers.
If is often said that the Church has, in fact, only very rarely defined the precise meaning of a biblical passage. Whether or not that is true one clear instance of such a definition is the Bull Unam Sanctam which has very precise teaching concerning Luke 22:35-38 and John 18:11. In ordering the disciples to buy a sword if they had not one already, and in telling them that two swords are enough, and in ordering Peter to sheath his sword Our Lord laid out the precise nature of the jurisdiction of the sacramental hierarchy and the Supreme Pontiff over the temporal power.
Both the temporal and the spiritual power are intrinsic to the Church. The spiritual sword is to be exercised for the specific ends for which the Church was instituted and by the members of the ecclesiastical hierarchy. In contrast, the temporal sword must be exercised by members of the Church but cannot be wielded by the members of the ecclesiastical hierarchy (although they may confiscate it if it is misused and assign it to another) because it is not a means by which the specific ends of the Church may be advanced.
What rarely seems to attract much notice is the reason Our Lord gave for this arrangement:
And he said to them: When I sent you without purse, and scrip, and shoes, did you want anything? But they said: Nothing. Then said he unto them: But now he that hath a purse, let him take it, and likewise a scrip; and he that hath not, let him sell his coat, and buy a sword. For I say to you, that this that is written must yet be fulfilled in me: And with the wicked was he reckoned. For the things concerning me have an end. But they said: Lord, behold here are two swords. And he said to them, It is enough.
The apostles are told to obtain a sword because Christ will be treated as a criminal. As Our Lord also said at the Last Supper “the servant is not greater than his master. If they have persecuted me, they will also persecute you: if they have kept my word, they will keep yours also.” The opposition between the Church and the world is such that the Apostles (and their successors) need to have the protection of force in order to function. Yet, a short time later when Peter uses his sword to try to defend the Lord he is rebuked. “Put up thy sword into thy scabbard”. The Apostles have two swords but they are permitted to wield only one. The word of God is in the power of the clergy the state is to be in the power of the laity.
How does this fit with the prohibition on coercive conversion? The temporal sword of Christendom is essentially defensive. It is not ‘for’ the Church as Boniface VIII insists, it is wielded ‘by’ the Church (the lay faithful). The essential purposes of the Church cannot be advanced by violence but the non-ordained members of the Church can use the temporal sword to defend the Church from external persecution. Once the state is no longer in the hands of the Church this is not possible. So long as the state is non-Christian the Church’s business lies in buying the sword (bringing the temporal order by consent into the possession of the Church). Once it is purchased the sword may be drawn – but only by the laity – to stave off temporal impediments to the operation of the spiritual sword. We do not live by the sword. The life of Christendom is established and maintained by the peaceful spreading of the Gospel. However, once that life has reached the highest temporal level of social organisation the temporal sword can and should be drawn in its defence.
As St Cyril of Alexandria teaches:
He says sell his cloak, and buy a sword: for henceforth the question with all those who continue in the land will not be whether they possess anything or not, but whether they can exist and preserve their lives. For war shall befall them with such unendurable impetuosity, that nothing shall be able to stand against it.
At the beginning of the Song of Roland Charlemagne (in deference to his council) seeks to negotiate a temporal peace with Islam. He seeks to keep his cloak instead of buying a sword. He forgets the truth that he remembers later in the midst of battle with the Emir of Babylon: “Never to Paynims may I show love or peace.” The Lord tells us “the things concerning me have an end” there is no new revelation to dispense us from the unremitting opposition of the world. As Leo XIII teaches “Christians are born for combat”. The faithful must sell their cloaks and buy a sword because the state cannot simply be left in the hands of the pagans if the Church is to survive. This is why the Song ends with a weary Emperor roused from his bed by St Gabriel to carry on the war. He sought not first the Kingdom of God and His justice and so earthly peace is taken from him until he learns his lesson.