Ephesians 4:4–6 (CSB) — 4 There is one body and one Spirit—just as you were called to one hope at your calling—5 one Lord, one faith, one baptism, 6 one God and Father of all, who is above all and through all and in all.
Christian epistemology holds “oneness” in high esteem and depends on the Biblical construct of “oneness” to uphold its theology. Unfortunately, much of our theological understanding of epistemological “oneness” has been lost because of the divisions that have divided the body. We can readily see from Scripture that if the Bible says that there is “one Spirit”, then it also says that there is “one body” (i.e. one Church). But in loosing our grasp of Biblical “oneness” to the errors of division, we seem to have forgotten that there is one Spirit.
By no means am I suggesting that anyone is intellectually professing that there are more than one divine spirits of deity. No, but we have lost the evidencial knowledge of what it means that there is “one Spirit”. When we enter a church from a certain brand of Christianity down the street, we “see”, “hear”, and “experience” a completely different “version” of the “spirit” from the one that we would encounter in the church across the street. What I mean by this is that some people’s version of the “spirit” is entirely abstract and intellectual; he exists in the ethereal. While others depict the “spirit” as experiential and entirely disconnected from any objective truths (Biblical or otherwise).
The Christian confession is that there is “one body and one Spirit”. When we unnecessarily divide from one another, we lose something of the Holy Spirit that Scripture ties inextricably to the unity of the Christian Church.
Cyril of Alexandria portrayed the oneness of the Holy Spirit in this manner:
Christ breathed the Spirit in a corporeal fashion and thus showed that as from the mouth of a man comes the corporeal breath, so from the divine substance in a way that befits it comes the breath that proceeds from it.
Cyril of Alexandria, Comm. on John 14.16, tractate IX, MPG 74.258 (pp. 34–36)
Because there is one God and one Lord, there must also be one Spirit who inhabits one body! The Holy Spirit was breathed out from the divine to the degree that this communicates the Holy Spirit proceeding from God (John 15:26). He does not proceed from the Father in part, nor in degrees, but fully as one Spirit proceeding from one God. The Spirit is, therefore, none other than the One God who has met Israel as Yahweh, the God of Israel, God of Hosts, Spirit of Yahweh (Num. 11:29; Judg. 3:10; Ps. 139:7; Isa. 61:1).
Both Ambrose and Augustine uphold this ancient faith:
For the Holy Spirit is not subject to any foreign power or law, but is the Arbiter of His own freedom, dividing all things according to the decision of His own will to each”
Ambrose, Of the Holy Spirit, prologue.l8, NPNF 2 X, (p. 96)
For he is called properly what they are called in common, because the Father is a spirit and the Son is a spirit, and the Father is holy and the Son is holy. In order that the communion between them might be signified by a name which is appropriate to both, the Holy Spirit is called the gift of both.
Augustine, Trin. V.11, FC 45, (p. 190)