The soul of Jesus is rational and of the same substance as human souls
Eustathius of Antioch is opening his interpretation of Psalm 15 by arguing that Jesus possessed a human soul as well as human flesh.
But surely the soul of Jesus had experience of both. For it came to be in the region of human souls, and having come to be outside the flesh it lives and subsists. It is therefore rational and of the same substance as the souls of human beings, just as his flesh is of the same substance as human flesh, having come forth from Mary.
From the interpretation of Psalm 15 by Eustathius of Antioch: “God sent his Son, born of a woman” (Galatians 4:4). He did not say “born ones,” but “born”—for the person is singular. I did not say the nature is singular; away with it, may it not be! Nor did I say that flesh and divinity have the same substance. But I said one Lord Jesus Christ, through whom all things exist, known in every way in the distinction of natures.
Greek
Commentarius in Psalmum [Sp.] (fragmenta) ̓Εκ τῆς ἑρμηνείας τοῦ ιεʹ ψαλμοῦ· Ἀλλὰ μὴν ἡ τοῦ Ἰησοῦ ἑκατέρων πεῖραν ἔσχε. Γέγονε γὰρ καὶ ἐν τῷ χωρίῳ τῶν ἀνθρωπίνων ψυχῶν, καὶ τῆς σαρκὸς ἐκτὸς γενομένη ζῇ καὶ ὑφέστηκε. Λογικὴ ἄρα, καὶ ταῖς ψυχαῖς τῶν ἀνθρώπων ὁμοούσιος, ὥσπερ καὶ ἡ σὰρξ ὁμοούσιος τῇ τῶν ἀνθρώπων σαρκὶ τυγχάνει, ἐκ τῆς Μαρίας προελθοῦσα. Εὐσταθίου Ἀντιοχείας ἐξ ἑρμηνείας τοῦ ιεʹ ψαλμοῦ· Ἐξαπέστειλεν ὁ θεὸς τὸν υἱὸν αὐτοῦ γενόμενον ἐκ γυναικός· οὐ γενομένους, ἀλλὰ γενόμενον· μοναδικὸν γὰρ τὸ πρόσωπον· οὐκ εἶπον μοναδικὴν τὴν φύσιν· ἄπαγε, μὴ γένοιτο· οὐδὲ τὴν αὐτὴν οὐσίαν σαρκὸς καὶ θεότητος, ἀλλ' εἶπον ἕνα Κύριον Ἰησοῦν Χριστὸν, δι' οὗ τὰ πάντα, ἐν τῷ διαφόρῳ τῶν φύσεων, γνωριζόμενον κατὰ πάντα.