DE MONARCHIA OF DANTE ALIGHIERI
CHAPTER IX: Argument from the two swords.
1. They quote also the words in Luke which Peter addressed to Christ, saying, "Behold, here are two swords,"  and they assert that the two ruling powers were predicted by those two swords, and because Peter declared they were "where he was," that is, "with him," they conclude that according to authority these two ruling powers abide with Peter's successor.
2. To refute this we must show the falsity of the interpretation on which the argument is based. Their assertion that the two swords which Peter designated signify the two ruling powers before spoken of, we deny outright, because such an answer would have been at variance with Christ's meaning, and because Peter replied in haste, as usual, with regard to the mere external significance of things.
3. A consideration of the words preceding it and of the cause of the words will show that such an answer would have been inconsistent with Christ's meaning. Let it be called to mind that this response was made on the day of the feast, which Luke mentions earlier, saying, "Then came the day of unleavened bread, when the passover must be killed."  At this feast Christ had already foretold His impending passion, in which He must be parted from His disciples. Let it be remembered also that when these words were uttered, all the twelve disciples were together; wherefore a little after the words just quoted Luke says, "And when the hour was come, He sat down, and the twelve Apostles with him."  Continuing the discourse from this place he reaches the words, "When I sent you without purse, and scrip, and shoes, lacked ye anything?"  And they answered, "Nothing." Then said He unto them, "But now, he that hath a purse, let him take it, and likewise his scrip: and he that hath no sword, let him sell his garment, and buy one." The meaning of Christ is clear enough here. He did not say, "Buy or procure two swords," but "twelve;" for it was in order that each of the twelve disciples might have one that He said to them, "He that hath no sword, let him buy one." And He spake thus to forewarn them of the persecution and contempt the future should bring, as though he would say, "While I was with you ye were welcomed, now shall ye be turned away. It behooves you, therefore, to prepare for yourselves those things which before I denied to you, but for which there is present need." If Peter's reply to these words had carried the meaning ascribed to it, the meaning would have been at variance with that of Christ, and Christ would have censured Him, as he did oftentimes, for his witless answers. However, He did not do so, but assented, saying to him, "It is enough,"  meaning, "I speak because of necessity; but if each cannot have a sword, two will suffice."
4. And that Peter usually spoke of the external significance of things is shown in his quick and unthinking presumption, impelled, I believe, not only by the sincerity of his faith, but by the purity and simplicity of his nature. To this characteristic presumption all those who write of Christ bear witness.
5. First, Matthew records that when Jesus had inquired of the disciples: "Whom say ye that I am?" before all the others Peter replied, "Thou art Christ, the Son of the living God." He also records that when Christ was telling His disciples how He must go to Jerusalem and suffer many things, Peter took Him and began to rebuke Him, saying, "Be it far from thee, Lord: this shall not be unto thee." Then Christ, turning to him, said in reproof, "Get thee behind me, Satan."  Matthew also writes that on the Mount of Transfiguration, in the presence of Christ, Moses, and Elias, and the two sons of Zebedee, Peter said, "Lord, it is good for us to be here. If thou wilt, let us make here three tabernacles, one for thee, one for Moses, and one for Elias."  Matthew further writes that when the disciples were on the ship in the night, and Christ walked on the water, Peter said, "Lord, if it be thou, bid me come unto thee on the water."  And that when Christ predicted how all His disciples should be offended because of Him, Peter answered, "Though all men shall be offended because of thee, yet will I never be offended."  And afterwards, "Though I should die with thee, yet will I not deny thee." And this statement Mark  confirms, while Luke writes that, just before the words we have quoted concerning the swords, Peter had said to Christ, "Lord, I am ready to go with thee, both into prison and to death." 
6. John tells of him, that when Christ desired to wash his feet, Peter asked, "Lord, dost thou wash my feet?" and then said, "Thou shalt never wash my feet."  He further relates how Peter smote with his sword the servant of the High Priest, an account in which the four Evangelists agree.  And John tells how when Peter came to the sepulchre and saw the other disciples lingering at the door, he entered in straightway;  and again when after the resurrection Jesus stood on the shore and Peter "heard that it was the Lord, he girt his fisher's coat unto him (for he was naked), and did cast himself into the sea."  Lastly, he recounts that when Peter saw John, he said to Jesus, "Lord, and what shall this man do?" 
7. It is a source of joy to have summed up this evidence of our Head Shepherd,  in praise of his singleness of purpose. From all this it is obvious that when he spoke of the two swords, his answer to Christ was unambiguous in meaning.
8. Even if the words of Christ and Peter are to be accepted typically, they cannot be interpreted in the sense these men claim, but rather as referring to the sword concerning which Matthew writes: "Think not that I am come to send peace on earth: I came not to send peace, but a sword. For I am come to set a man at variance against his father,"  and what follows. This He accomplished in word and deed, wherefore Luke tells Theophilus of all "that Jesus began to do and teach."  Such was the sword Christ enjoined them to buy, and Peter made answer that already they had two with them. As we have shown, they were ready for words and for works to bring to pass those things which Christ proclaimed He had come to do by the sword.
1. Luke 22. 38. This was one of the most popular arguments in mediaeval writers for the supremacy of the Church. In the bull "Unam Sanctam" Boniface VIII says: "We are taught by the words of the gospel to recognize that two swords are in the power of this man, that is, the spiritual and temporal. For when the apostles said, 'Here are two swords,' the Lord did not respond, 'It is too much,' but, 'It is enough.' Both are in the power of the Church: the one the spiritual, to be used by the Church, the other the material, for the Church; the former that of priests, the latter that of kings and soldiers, to be wielded at the command and by the sufferance of the priest. One sword must be under the other, the temporal under the spiritual.... The spiritual instituted the temporal power, and judges whether that power is well exercised.... We therefore assert, define, and pronounce that it is necessary to salvation to believe that every human being is subject to the Pontiff of Rome."
Generally with Dante the sword typifies Empire. Purg. 16. 109: "The sword is joined with the crook." Par. 8. 145: "But ye wrest to religion such an one as shall have been born to be girt with the sword, and ye make him a king who is a man of sermons."
2. Luke 22. 7.
3. Luke 22. 14.
4. Luke 22. 35, 36.
5. Luke 22. 38.
6. Matt. 16. 15, 16, 21, 22, 23.
7. Matt. 17. 4.
8. Matt. 14. 28. Peter's faith on this occasion is the subject of praise again in Par. 24. 34: "O eternal light of the great man to whom our Lord left the keys, which he bore below, of this wondrous joy, try this man concerning points easy and hard as pleases thee, about the faith by which thou didst go upon the sea."
9. Matt. 26. 33, 35.
10. Mark 14. 29.
11. Luke 22. 33.
12. John 13. 6, 8.
13. John 18. 10; Matt. 26. 51; Marl 14. 47; Luke 22. 50.
14. John 20. 5, 6. Dante's second reference to this incident is in Par. 24. 125: "O holy father, O spirit who seest that which thou so believest, that thou didst outdo younger feet toward the sepulchre."
15. John 21. 7.
16. John 21. 21.
17. "Head Shepherd" is in the Latin "Archimandrita." St. Francis is given this name Par. 11. 99: "The holy desire of this head shepherd of his flock was crowned with a second diadem by the eternal spirit through Honorius." And in Letter 9. 6 Dante calls the unfaithful officers of the Church, "Archimandrites throughout the world in name alone."
18. Matt. 10. 34, 35.
19. Acts 1. 1.