The Holy Spirit was another Comforter differing not in nature, but in operation. For whereas our Savior in his office of Mediator, and of Messenger,and as High Priest, made supplication for our sins, the Holy Spirit is a Comforter in another sense, that is, as consoling our griefs. But do not infer from the different operations of the Son and the Spirit a difference of nature.

—Didymus the Blind, On the Holy Spirit 27