Potamius of Lisbon - made easier to read.
(For heavenly/earthly witnesses, I simply BOLD the text, so the reader can see the context without Conti or me placing in a verse number.)
● Letter to Athanasius the Bishop of Alexandria on the consubstantiality of the Son of God. You must justly admit that, when your poisonous desire of impure slander was inflamed, the venerable fathers transfixed you with pious arrows in that holier council. Here also it is clearly shown that you held before you fetters of malicious distortion, since the Savoir says: "I have come down from heaven not to do my own will but the will of him who sent him." (John 6:38) What do you answer, serpent? Is it really possible that you seek to obfuscate the brightness of this [PAGE 138] pure profession, which they consider to be a very small problem? The occasion has a bearing on the matter. The Lord our Savior appeared to mankind as a human being, since he had clothed himself with a human body. Therefore, he said: "I have come down from heaven not to do my own will." (John 6:38) He denied the exercise of the humanity that was in him. Therefore, he cries out in order to proclaim in himself the predecessor whom he remembers as his Father and begetter. Since the Son is named second, therefore he who precedes is greater: but, because "these three are one", the substance of him who sends and of him who is sent, in the context of the unity of the Godhead, is one: "I and the Father are one." (John 10:30), and "He sees me, sees the Father." (John 14:9) and, as the Savoir himself said to the Apostles: "I have been so long with you and yet you do not know the Father." (John 14:9)
(Potamius of Lisbon. "Letter to Athanasius the Bishop of Alexandria on the consubstantiality of the Son of God" in the life and works of Potamius of Lisbon edited and translated by Marco Conti, 1998, p. 136)
● Letter on the Substance of the Father and the Son and the Holy Spirit. 3. With good reason John asserts: 'and the three of them are one' 'Substance ' is the expression of a single entity. In fact the substance of a thing is the totality of that through which a thing exists. Thus 'substance' will set a certain condition under a certain authority, or shows that a certain condition is subjected to it. As a consequence 'substance' is that through which the perplexity of faith is resigned and the unity of the Trinity is bound together.
(Potamius of Lisbon. "Letter on the Substance of the Father and the Son and the Holy Spirit" in the life and works of Potamius of Lisbon edited and translated by Marco Conti, 1998, p. 150)
● Letter on the Substance of the Father and the Son and the Holy Spirit. 10. And now, if you agree, since we have burst out from the spring of the Trinity, let us examine again, like keen investigators, the innermost nature of the 'substance', from which the spring gushes and flows out. Thus the Savior proclaimed: 'The Father and I are one' (John 10:30). Likewise John says: "And the three of them are one'. And David also: "For this purpose God has anointed you, your God' (Ps. 44:8) he says - that is, the God to whom David's words, the half of your part of which he is the whole. 'Yours' - he says - that is devoted to you, to whom your yourself should be made over. He is 'yours' to whom the words are spoken, or 'his' who comes, or 'of him' whom he frequently meets.'Your God', he says, to whom you certainly belong, with whom you are associated thanks to unity, or who, from his 'substance', is associated with you. But since the power of the Father is the Son, the power itself pertains to its 'substance', because 'substance' cannot exist without power. With good reason the 'substance' of the Father and the Son is one.
(Potamius of Lisbon. "Letter on the Substance of the Father and the Son and the Holy Spirit" in the life and works of Potamius of Lisbon edited and translated by Marco Conti, 1998, p. 156)
● Letter on the Substance of the Father and the Son and the Holy Spirit. 19. What the Son made, the Father caused. What the Father wanted, the Son fulfilled. The Father ordered all that the Son commanded. The will of the Father is everything for which the Son feels compassion: in fact the Word of God, Christ, that is the power of the Father, has put everything into effect. That is why the Father has made all that the Son has ordered. Indeed the Father with his power, when the Son descended to the underworld, through the Son and his self-same power, broke the adamantine bars of hell, and with the word of power evoked the dead men from the bowels of the abyss, and with the flaming sword of his mouth, according to the judgement delivered by his Christ, exiled the devil. This is one substance, this is the invisible and eternal majesty, this is the everlasting unity of the undivided Trinity. As John says: 'And the three of them are one'. And Peter implores 'three tabernacles' (Mark. 9:4), and 'every word is confirmed by three witnesses' (Matt. 18:16).
(Potamius of Lisbon. "Letter on the Substance of the Father and the Son and the Holy Spirit" in the life and works of Potamius of Lisbon edited and translated by Marco Conti, 1998, p. 162)
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DIFFERENCES IN TWOGIG Aug 2022
[Epistula de Substantia] For the Son has expressed the will of the Father, since everything has been
carried out by the word of God, Christ, that is to say, the power of the Father. Hence it follows that the
Father did what the Son ordered. For the Father with his power, when the Son descended into hell,
through the Son and with the same power, he broke the steel bars of Tartarus and with the word of his
own power brought the dead from the depths of hell and with the flaming spear from his mouth sent the
devil into exile through the order given by his Christ. This is one substance, this is the undivided
and eternal majesty, this is the everlasting unity of the undivided Trinity. As John says: "And
the three are one." (1 John 5:7) And Peter asks for "three tents" and "every word is fixed with
three witnesses" (Potamius of Lisbon, Epistula de Substantia Patris et Filii et Spiritus Sancti)
o Latin: Quod Filius fecit, Pater operatus est. Quod Pater voluit implevit et Filius. Pater iussit
quicquid Filius imperavit. Patris voluntas est quicquid Filius miseretur: omnia enim verbum dei,
Christus, hoc est virtus Patris, exercuit, inde est, quod Pater fecit quicquid Filius ordinavit. Pater
enim virtute sua, descendente ad inferos Filio, per filium eademque virtute adamantinas tartari
seras infregit, et verbo virtutis de secretis barathri mortuos evocavit, et diabolum flammea oris
romphea Christi sui per sententiam exulavit. Haec est una substantia, haec invisibilis et
aeterna maiestas, haec indiscissae Trinitatis unitas sempiterna.
Ut Iohannes ait: 'Et tres unum sunt' (I Ioh. 5:7). Et 'tria tabernacula' Petrus exorat (Marc. 9:4), et 'tribus testibus verbum omne consistit (Matt. 18:16).
(Potamius of Lisbon, Epistula de Substantia Patris et Filii et Spiritus Sancti, 19; Latin text: Yarza Urkiola, Potamio de Lisboa, Epistula de substantia, 1999, p. 291)