The Nicene faith is catholic and apostolic, and sufficient on the Spirit
Amphilochius, writing on behalf of a synod, is answering the recipients' inquiry about the faith by affirming the Nicene creed and explaining why the fathers said nothing more extensive about the Holy Spirit.
We recognize the holy synod of the fathers at Nicaea as truly catholic and apostolic, and we guard the faith set forth by the fathers at that time, praying that it may remain unmoved and unshaken forever. It became necessary then for the fathers to explain more fully the glory of the Only Begotten, because they were eager to cut off the recently sprouting heresy of Arius, cutting away its first seeds beforehand, before the thorn became fully hardened. But since the question concerning the Spirit was then still silenced, they added nothing more extensive about it. Yet for those who read intelligently, the teaching about the Spirit in that creed is sufficient. Just as they decreed belief in the Father and the Son, so also they decreed belief in the Spirit, neither introducing any other nature into the divine and blessed Trinity nor cutting off any member of the Trinity from the statement of faith. But since Satan, attempting afresh to shake the churches, has cast into some people doubt about the Spirit, it is necessary to run back to the source of the faith from which the fathers at Nicaea drew when they made their statement of faith. What, then, is the perfection of our faith?
Greek
Τὴν ἁγίαν σύνοδον τῶν πατέρων τῶν ἐν Νικαίᾳ σύνοδον
ὄντως καθολικὴν καὶ ἀποστολικὴν γνωρίζομεν, καὶ πίστιν τὴν ἐκτεθεῖσαν ὑπὸ τῶν πατέρων τηνικαῦτα φυλάττομεν ἀκίνητον καὶ πρὸς τὸ διηνεκὲς ἀσπάρακτον μένειν εὔχομαι. Γέγονε δὲ τότε τοῖς πατράσιν ἀναγ καιότερον πλατύτερον ἐξηγήσασθαι περὶ τῆς δόξης τοῦ μονογε νοῦς, ἐπειδὴ τότε νεωστὶ φυομένην τὴν αἵρεσιν τοῦ Ἀρείου διὰ σπουδῆς ἔσχον ἐκκόψαι τὰ πρῶτα αὐτῆς προαναιροῦντες σπέρ ματα, πρὶν τελέως ἐκτραχυνθῆναι τὴν ἄκανθαν. Σεσιγημένου δὲ τηνικαῦτα τοῦ κατὰ τὸ πνεῦμα ζητήματος διὰ τοῦτο πλατύτερον μὲν οὐδὲν προσέθεσαν· τοῖς μέντοι γε συνετῶς ἀναγινώσκουσιν αὐτάρκης καὶ ἡ περὶ τοῦ πνεύματος ἐν ἐκείνῃ τῇ πίστει διδασκα λία. Ὥσπερ εἰς πατέρα καὶ υἱὸν πιστεύειν, οὕτω καὶ εἰς τὸ πνεῦμα πιστεύειν ἐδογμάτισαν, μήτε ἑτέραν τινὰ φύσιν ἐπεισάγοντες τῇ θείᾳ καὶ μακαρίᾳ τριάδι μήτε τι τῶν ἐκ τῆς τριάδος ἀποτέμνοντες εἰς τὴν τῆς πίστεως ἔκθεσιν. Ἐπεὶ δὲ πρόσφατον ὁ σατανᾶς διασαλεύειν τὰς ἐκκλησίας ἐπιχειρῶν ἐνέβαλέ τισι περὶ τοῦ πνεύματος δισταγμόν, ἀναγκαῖον ἐπὶ τὴν πηγὴν ἀνατρέχειν τῆς πίστεως ἐξ ἧς καὶ οἱ κατὰ Νίκαιαν πατέρες ἀναρυσάμενοι τὴν ἔκθεσιν τῆς πίστεως ἐποίησαν. Τίς οὖν ἡμῶν ἡ τῆς πίστεως τελειότης;