Book III, Chapter XV

Again, that which is contrary to the nature of a thing cannot be counted as one of its essential powers; for the essential powers of each individual follow on its nature, in order to gain its end. But the power to grant authority in that which is the realm of our mortal state is contrary to the nature of the Church.¹ Therefore it is not in the number of its essential powers. For the proof of the minor premiss we must know that the nature of the Church means the form [or essence]² of the Church. For although men use the word nature not only of the form of a thing, but also of its matter, nevertheless, it is of the form that they use it more properly, as is proved in the book "of Natural Learning."³ But the [essence or] form of the Church is nothing else than the life of Christ, as it is contained both in His sayings and in His deeds. For His life was the example and ideal of the militant Church, especially of its pastors, and above all of its chief pastor, to whom it belongs to feed the sheep and the lambs of Christ. And therefore when Christ left His life unto men for an example He said in John's Gospel: "I have given you an example that ye should do as I have done to you." And He said unto Peter specially, after that He had committed unto him the office of shepherd, the words which John also reports: "Peter, follow me." But Christ denied before Pilate that His rule was of this sort, saying: "My kingdom is not of this world: if my kingdom were of this world, then would my servants fight, that I should not be delivered to the Jews; but now is my kingdom not from hence."⁴

But this saying must not be understood to mean that Christ, who is God, is not the lord of this kingdom, for the Psalmist says: "The sea is His, and He made it, and His hands formed the dry land."⁵ We must understand it to mean that, as the pattern of the Church, He had not the care of this kingdom. It is as if a golden seal were to speak of itself, and say: "I am not the standard for such and such a class of things;" for in so far as it is gold, this saying is untrue, seeing that gold is the standard of all metals; but it is true in so far as it is a sign capable of being received by impression.

It belongs, then, to the very form of the Church always to speak the same, always to think the same; and to do the opposite of this is evidently contrary to its essential form--that is to say, to its nature. And from this it may be collected that the power of bestowing authority on this kingdom is contrary to the nature of the Church; for contrariety which is in thought or word follows from contrariety which is in the thing thought and the thing said; just as truth and falsehood in speech come from the being or the not-being of the thing, as we learn from the doctrine of the Categories. It has then become manifest enough by means of the preceding arguments, by which the contention of our opponents has been shown to lead to an absurd result, that the authority of the Empire is not in any way dependent on the authority of the Church.