Letter 138: Those who fail conspicuously at what is universally acknowledged to be right have no authority to pronounce on...

To Didymus. On the words, "I and the Father are one." [John 10:30] It is not the case, as you wrote, that one sees in [...] a light hidden by Scripture, through the things you have indicated; rather, one is blinded before the radiance that flashes out from it. For to say that what appears is one, the hypostasis of Father and of Son being one within it, is a mark of great folly, or rather of madness. For if you attend carefully to the exactness of what is written, you will find the unerring truth of the mystery. "I and the Father are one," it says; not, "I and the Father am one." The word "one" [ἕν, neuter], then, is indicative of the one essence; the word "we are" [ἐσμέν, plural] is significative of the two hypostases.

Εἰς τὸ, «Ἐγὼ καὶ ὁ Πατὴρ ἕν ἐσμεν.» Οὐκ ἔστιν, ὡς ἔγραψας, ἰδεῖν τὸ ἐν (33). Γραφὴ κρυπτόμενον φῶς, δι’ ὧν ἐδήλωτας, ἀλλὰ μᾶλλον τυφλώττει πρὸς τὴν αἴγλην τὴν ἐξ αὐτῆς ἀστράπτουσαν. Τὸ γὰρ εἰπεῖν μίαν εἶναι φαινομένην, ἐν αὐτῇ Πατρὸς καὶ Υἱοῦ τὴν ὑπόστασιν, μεγάλης εἶναι ἀνοίας, μᾶλλον δὲ ἐμβροντησίας. Εἰ γὰρ πρόσεχῃς ἀκριβῶς τῇ ἀσφαλείᾳ τῶν γεγραμμένων, εὑρήσεις τὸ ἀπλανὲς τοῦ μυστηρίου. «Ἐγὼ καὶ ὁ Πατὴρ ἕν ἐσμεν,» εἴρηται· οὐκ, «Ἐγὼ καὶ ὁ Πατὴρ ἕν εἶμι.» Τὸ τοίνυν ἕν τῆς μιᾶς οὐσίας δηλωτικόν· τὸ ἐσμέν, τῶν δύο ὑποστάσεων σημαντικόν.