John 10:30

(viii. de Trin. c. 5) The heretics, since they cannot gainsay these words, endeavour by an impious lie to explain them away. They maintain that this unity is unanimity only; a unity of will, not of nature; i. e. that the two are one, not in that they are the same, but in that they will the same. But they are one, not by any economy merely, but by the nativity of the Son's nature, since there is no falling off of the Father's divinity in begetting Him. They are one whilst the sheep that are not plucked out of the Son's hand, are not plucked out of the Father's hand: whilst in Him working, the Father worketh; whilst He is in the Father, and the Father in Him. This unity, not creation but nativity, not will but power, not unanimity but nature accomplisheth. But we deny not therefore the unanimity of the Father and Son; for the heretics, because we refuse to admit concord in the place of unity, accuse us of making a disagreement between the Father and Son. We deny not unanimity, but we place it on the ground of unity. The Father and Son are one in respect of nature, honour, and virtue: and the same nature cannot will different things.

(Tract. xxxvi. non occ.) Mark both those words, one and are, and thou wilt be delivered from Scylla and Charybdis. In that He says, one the Arian, in we are the Sabellian, is answered. There are both Father and Son. And if one, then there is no difference of persons between them. (vii. de Trin. c. 2) We are one. What He is, that am I, in respect of essence, not of relation.

How are the Father and the Son inseparable, since Himself said, "I and the Father are one?" Because the Father and the Son are not two Gods, but one God, the Word and He whose the Word is, One and the Only One, Father and Son bound together by charity, One God, and the Spirit of Charity also one, so that Father, Son, and Holy Spirit is made the Trinity. Therefore, not only of the Father and Son, but also of the Holy Spirit; as there is equality and inseparability of persons, so also the works are inseparable. I will tell you yet more plainly what is meant by "the works are inseparable." The catholic faith does not say that God the Father made something, and the Son made some other thing; but what the Father made, that also the Son made, that also the Holy Spirit made. For all things were made by the Word; when "He spoke and they were done," it is by the Word they were done, by Christ they were done.

But that there may be no more room for hesitation, hear what follows: "I and my Father are one." Up to this point the Jews were able to bear Him; they heard, "I and my Father are one," and they bore it no longer; and hardened in their own way, they had recourse to stones. "They took up stones to stone Him." ...And they answered, "For a good work we stone thee not, but for blasphemy, and because that thou, being a man, makest thyself God." Such was their reply to His words, "I and my Father are one." You see here that the Jews understood what the Arians understand not. For they were angry on this account, that they felt it could not be said, "I and my Father are one," save where there was equality of the Father and the Son.

He only means His perfect agreement with His Father.