The Holy Ghost, then, always existed, and exists, and always will exist. He neither had a beginning, nor will He have an end; but He was everlastingly ranged with and numbered with the Father and the Son. For it was not ever fitting that either the Son should be wanting to the Father, or the Spirit to the Son. For then Deity would be shorn of Its Glory in its greatest respect, for It would seem to have arrived at the consummation of perfection as if by an afterthought. Therefore He was ever being partaken, but not partaking; perfecting, not being perfected; sanctifying, not being sanctified; deifying, not being deified; Himself ever the same with Himself, and with Those with Whom He is ranged; invisible, eternal, incomprehensible, unchangeable, without quality, without quantity, without form, impalpable, self-moving, eternally moving, with free-will, self-powerful, All-powerful (even though all that is of the Spirit is referable to the First Cause, just as is all that is of the Only-begotten); Life and Lifegiver; Light and Lightgiver; absolute Good, and Spring of Goodness; the Right, the Princely Spirit; the Lord, the Sender, the Separator; Builder of His own Temple; leading, working as He wills; distributing His own Gifts; the Spirit of Adoption, of Truth, of Wisdom, of Understanding, of Knowledge, of Godliness, of Counsel, of Fear (which are ascribed to Him) by Whom the Father is known and the Son is glorified; and by Whom alone He is known; one class, one service, worship, power, perfection, sanctification. Why make a long discourse of it? All that the Father hath the Son hath also, except the being Unbegotten; and all that the Son hath the Spirit hath also, except the Generation. And these two matters do not divide the Substance, as I understand it, but rather are divisions within the Substance.
-Gregory of Nazianzus, On Pentecost (Oration XLI)