Book of Saint Basil On the Spirit

“The heresy of Arius lowered the dignity of the Holy Ghost as well as that of the Son. He taught that the Three Persons of the Holy Trinity are wholly unlike one another both in essence and in glory... But the Nicene definition, while it was precise in regard to the Son, left the doctrine of the Holy Ghost comparatively open, (Πιστεύομεν εἰς τὸ "Aycov Πνεῦμα, ) not from hesitation or doubt, but because this side of Arian speculation was not prominent...(In 374) Amphilochius, the first cousin of Gregory of Nazianzus and friend and spiritual son of Basil, paid the first of his annual autumn visits to Caesarea (Bishop Lightfoot, D.C.B. i. 105) and there urged St. Basil to clear up all doubt as to the true doctrine of the Holy Spirit by writing a treatise on the subject. St. Basil complied, and, on the completion of the work, had it engrossed on parchment (Letter ccxxx1.) and sent it to Amphilochius, to whom he dedicated it…” From Preface to The Book of Saint Basil On the Spirit.