Why the Nicene wording was chosen
Athanasius is explaining the reasoning behind the Nicene Council's choice of the phrase 'from the substance' and the scriptural terms it gathered, against the evasions of Eusebius and his party.
For it is not the words themselves that grieve them, but the condemnation of them that took place in those words. And again they themselves have been the cause of this, and even if they want to hide it, though they know it, it is fitting for us to say it, so that from these things too the exactness with truth of the great council may be shown. For when the assembled bishops wanted to abolish the words of impiety invented by the Arians—the phrase “from nothing,” and calling the Son a creature and a thing made, and “there was when he was not,” and that he is of a changeable nature—and to write instead the words acknowledged from the Scriptures, that the Word is by nature the only-begotten from God, the power, the only wisdom of the Father, true God, as John said, and as Paul wrote, the radiance of his glory and the imprint of the Father’s actual being, the followers of Eusebius, dragged along by their own evil opinion, were saying to one another: “Let us agree. For we too are from God. For there is one God, from whom are all things (1 Corinthians 8:6), and, The old things have passed away; behold, all things have become new (2 Corinthians 5:17). And all things are from God.” They also considered what is written in the Shepherd: “First of all believe that there is one God, who created and ordered all things, and made them from what is not into being.” But the bishops, seeing their cunning and the evil craft of their impiety, expressed “from God” more clearly, and wrote that the Son is from the substance of God, so that created things, because they do not exist from themselves without a cause but have a beginning of coming into being, may be said to be from God, while the Son alone is proper to the Father’s substance. For this is proper to the only-begotten and true Word in relation to the Father. And this was the reason for writing “from the substance.”
Again, when the bishops were asking those who seemed to be few whether they would say that the Son is not a creature but the power, the only wisdom of the Father, and an eternal image, in all things unvarying from the Father, and true God, the followers of Eusebius were caught signaling to one another that these things also reach to us. “For we too,” they said, “are called the image and glory of God, and about us it is said, For we who live are always (2 Corinthians 4:11). And there are many powers. And all the power of the Lord went out from the land of Egypt. And the caterpillar and the locust are called a great power. And, The Lord of the powers is with us; the God of Jacob is our protector (Psalm 46:7 LXX (cf. "hosts" in Hebrew)). But we have the fact that we are God’s own, not simply, but because he also called us brothers. And if they say the Son is true God, it does not grieve us. For having come to be, he is true God.” This is the corrupted mind of the Arians. But here too the bishops, seeing their deceit, gathered from the Scriptures the radiance, the fountain and the river, and the imprint in relation to the actual being, and, In your light we shall see light (Psalm 36:9), and, I and the Father are one (John 10:30).
Greek
Οὐ γὰρ αἱ λέξεις αὐτοὺς λυποῦσιν, ἀλλ' ἡ ἐν αὐτῇ γενομένη κατάκρισις αὐτῶν. Καὶ τούτων δὲ πάλιν αἴτιοι γεγόνασιν αὐτοὶ, καὶ εἰ τοῦτο κρύπτειν αὐτοὶ θέλουσι, καίτοι γινώσκοντες, ἀλλ' ἡμᾶς ἀκόλουθον εἰπεῖν· ἵνα καὶ ἐκ τούτων ἡ μετὰ ἀληθείας ἀκρίβεια τῆς μεγάλης συνόδου δειχθῇ. Τῶν γὰρ συνελθόντων ἐπισκόπων βουλομένων τὰς μὲν παρὰ τῶν Ἀρειανῶν ἐφευρεθείσας τῆς ἀσεβείας λέξεις ἀν ελεῖν· τὸ Ἐξ οὐκ ὄντων· καὶ τὸ λέγειν κτίσμα καὶ ποίημα τὸν Υἱόν· καὶ, Ἦν ποτε, ὅτε οὐκ ἦν· καὶ ὅτι τρεπτῆς ἐστι φύσεως· τὰς δὲ τῶν Γραφῶν ὁμολογουμένας γράψαι· ὅτι τε ἐκ τοῦ Θεοῦ τῇ φύσει μονογενής ἐστιν ὁ Λόγος, δύναμις, σοφία μόνη τοῦ Πατρὸς, Θεὸς ἀληθινὸς, ὡς εἶπεν ὁ Ἰωάννης· καὶ ὡς ἔγραψεν ὁ Παῦλος, ἀπαύγασμα τῆς δόξης, καὶ χαρακτὴρ τῆς τοῦ Πατρὸς ὑποστάσεως· οἱ περὶ Εὐσέβιον, ὑπὸ τῆς ἰδίας κακοδοξίας ἑλκόμενοι, διελάλουν ἀλλήλοις· Συνθώμεθα· καὶ γὰρ καὶ ἡμεῖς ἐκ τοῦ Θεοῦ ἐσμεν· εἷς γὰρ Θεὸς, ἐξ οὗ τὰ πάντα· καὶ, Τὰ ἀρχαῖα παρῆλθεν, ἰδοὺ γέγονε τὰ πάντα καινά. Τὰ δὲ πάντα ἐκ τοῦ Θεοῦ. Ἐλογίζοντο δὲ καὶ τὸ ἐν τῷ Ποιμένι γραφέν· Πρῶτον πάντων πίστευ σον, ὅτι εἷς ἐστιν ὁ Θεὸς, ὁ τὰ πάντα κτίσας καὶ καταρτίσας, καὶ ποιήσας ἐκ τοῦ μὴ ὄντος εἰς τὸ εἶναι. Ἀλλ' οἱ ἐπίσκοποι, θεωρήσαντες τὴν πανουργίαν ἐκείνων, καὶ τὴν τῆς ἀσεβείας κακοτεχνίαν, λευκότερον εἰρήκασι τὸ ἐκ τοῦ Θεοῦ, καὶ ἔγραψαν, ἐκ τῆς οὐσίας τοῦ Θεοῦ εἶναι τὸν Υἱόν· ἵνα τὰ μὲν κτίσματα, διὰ τὸ μὴ ἀφ' ἑαυτῶν χωρὶς αἰτίου εἶναι, ἀλλὰ ἀρχὴν ἔχειν τοῦ γενέσθαι, λέγηται ἐκ τοῦ Θεοῦ· ὁ δὲ Υἱὸς μόνος ἴδιος τῆς τοῦ Πατρὸς οὐσίας· τοῦτο γὰρ ἴδιον μονογενοῦς καὶ ἀληθινοῦ Λόγου πρὸς Πατέρα. Καὶ περὶ μὲν τοῦ γεγράφθαι ἐκ τῆς οὐσίας ἡ πρόφασις αὕτη. Πάλιν δὲ τῶν ἐπισκόπων ἐρωτώντων τοὺς δοκοῦντας ὀλίγους, εἴπερ λέγοιεν, τὸν Υἱὸν οὐ κτίσμα, ἀλλὰ δύναμιν, σοφίαν μόνην τοῦ Πατρὸς, καὶ εἰκόνα ἀΐδιον, ἀπαράλλακτον κατὰ πάντα τοῦ Πατρὸς, καὶ Θεὸν ἀληθινὸν, κατελήφθησαν οἱ περὶ Εὐσέβιον διανεύοντες ἀλλήλοις, ὅτι καὶ ταῦτα φθάνει καὶ εἰς ἡμᾶς· καὶ γὰρ καὶ ἡμεῖς καὶ εἰκὼν καὶ δόξα Θεοῦ λεγόμεθα, καὶ περὶ ἡμῶν εἴρηται· Ἀεὶ γὰρ ἡμεῖς οἱ ζῶντες. Καὶ δυνάμεις πολλαί εἰσι· Καὶ ἐξῆλθε μὲν πᾶσα ἡ δύναμις Κυρίου ἐκ γῆς Αἰγύπτου. Ἡ δὲ κάμπη καὶ ἡ ἀκρὶς λέγεται δύναμις μεγάλη. Καὶ, Κύριος τῶν δυνάμεων μεθ' ἡμῶν, ἀντιλήπτωρ ἡμῶν ὁ Θεὸς Ἰακώβ. Ἀλλὰ γὰρ τὸ ἰδίους ἡμᾶς εἶναι τοῦ Θεοῦ ἔχομεν, οὐχ ἁπλῶς, ἀλλ' ὅτι καὶ ἀδελφοὺς ἡμᾶς ἐκάλεσεν. Εἰ δὲ καὶ Θεὸν ἀληθινὸν λέγουσι τὸν Υἱὸν, οὐ λυπεῖ ἡμᾶς· γενόμενος γὰρ, ἀληθινός ἐστιν. Αὕτη τῶν Ἀρειανῶν ἡ ἐφθαρμένη διάνοια. Ἀλλὰ καὶ ἐνταῦθα οἱ ἐπίσκοποι, θεωρήσαντες ἐκείνων τὸ δόλιον, συνήγαγον ἐκ τῶν Γραφῶν τὸ ἀπαύγασμα, τήν τε πηγὴν καὶ τὸν ποταμὸν, καὶ τὸν χαρακτῆρα πρὸς τὴν ὑπόστασιν, καὶ τὸ, Ἐν τῷ φωτί σου ὀψόμεθα φῶς· καὶ τὸ, Ἐγὼ καὶ ὁ Πατὴρ ἕν ἐσμεν.