Source for this translation:

Cardinal Henry Edward Manning, (Archbishop of Westminster, England), The Vatican Decrees in their Bearing on Civil Allegiance, (Catholic Publication Society: New York, 1875), p. 172-173.

Cardinal Manning's translation of Unam Sanctam:

Boniface, Bishop, Servant of the servants of God.
For perpetual remembrance :

1. Urged on by our faith, we are obliged to believe and hold that there is one holy, catholic, and apostolic Church. And we firmly believe and profess that outside of her there is no salvation nor remission of sins, as the bridegroom declares in the Canticles, " My dove, my undefiled, is but one; she is the only one of her mother; she is the choice one of her that bare her." And this represents the one mystical body of Christ, and of this body Christ is the head, and God is the head of Christ. In it there is one Lord, one faith, one baptism. For in the time of the Flood there was the single ark of Noah, which prefigures the one Church, and it was finished according to the measure of one cubit and had one Noah for pilot and captain, and outside of it every living creature on the earth, as we read, was destroyed.

2. And this Church we revere as the only one, even as the Lord says by the prophet, " Deliver my soul from the sword, my darling from the power of the dog." He prayed for his soul, that is, for himself, head and body. And this body he called one body, that is, the Church, because of the single bridegroom, the unity of the faith, the sacraments, and the love of the Church. She is that seamless shirt of the Lord which was not rent but was allotted by the casting of lots.

3. Therefore, this one and single Church has one head and not two heads, - for had she two heads, she would be a monster, - that is, Christ and Christ's Vicar, Peter and Peter's successor. For the Lord said unto Peter, " Feed my sheep." "My," he said, speaking generally and not particularly, " these and those," by which it is to be understood that all the sheep are committed unto him. So, when the Greeks or others say that they were not committed to the care of Peter and his successors, they must confess that they are not of Christ's sheep, even as the Lord says in John, " There is one fold and one shepherd."

4. That in her and within her power are two swords, we are taught in the Gospels, namely, the spiritual sword and the temporal sword. For when the Apostles said, "Lo, here," - that is, in the Church, - are two swords, the Lord did not reply to the Apostles " it is too much," but " it is enough." It is certain that whoever denies that the temporal sword is in the power of Peter, hearkens ill to the words of the Lord which he spoke, "Put up thy sword into its sheath." Therefore, both are in the power of the Church, namely, the spiritual sword and the temporal sword ; the latter is to be used for the Church, the former by the Church ; the former by the hand of the priest, the latter by the hand of princes and kings, but at the nod and sufferance of the priest.

5. The one sword must of necessity be subject to the other, and the temporal authority to the spiritual. For the Apostle said, " There is no power but of God, and the powers that be are ordained of God " ; and they would not have been ordained unless one sword had been made subject to the other, and even as the lower is subjected by the other for higher things. For, according to Dionysius, it is a divine law that the lowest things are made by mediocre things to attain to the highest. For it is not according to the law of the universe that all things in an equal way and immediately should reach their end, but the lowest through the mediocre and the lower through the higher.

6. But that the spiritual power excels the earthly power in dignity and worth, we will the more clearly acknowledge just in proportion as the spiritual is higher than the temporal. And this we perceive quite distinctly from the donation of the tithe and functions of benediction and sanctification, from the mode in which the power was received, and the government of the subjected realms. For truth being the witness, the spiritual power has the functions of establishing the temporal power and sitting in judgment on it if it should prove to be not good. [1] And to the Church and the Church's power the prophecy of Jeremiah attests: " See, I have set thee this day over the nations and the kingdoms to pluck up and to break down and to destroy and to overthrow, to build and to plant."

[1] This passage is based almost word for word upon Hugo de St. Victor, De Sacramentis, II. 2, 4.

7. And if the earthly power deviate from the right path, it is judged by the spiritual power; but if a minor spiritual power deviate from the right path, the lower in rank is judged by its superior ; but if the supreme power [the papacy] deviate, it can be judged not by man but by God alone. And so the Apostle testifies, "He which is spiritual judges all things, but he himself is judged by no man."

8. But this authority, although it be given to a man, and though it be exercised by a man, is not a human but a divine power given by divine word of mouth to Peter and confirmed to Peter and to his successors by Christ himself, whom Peter confessed, even him whom Christ called the Rock. For the Lord said to Peter himself, " Whatsoever thou shalt bind on earth," etc. Whoever, therefore, resists this power so ordained by God, resists the ordinance of God, unless perchance he imagine two principles to exist, as did Manichaeus, which we pronounce false and heretical. For Moses testified that God created heaven and earth not in the beginnings but " in the beginning."

9. Furthermore, that every human creature is subject to the Roman pontiff, - this we declare, say, define, and pronounce to be altogether necessary to salvation.