I recently read an essay by a leading evangelical theologian arguing that many "egalitarian" discussions of the doctrine of the Trinity threaten to compromise basic tenets of orthodox Christianity and to undermine, at least implicitly, the authority of the Bible (Wayne Grudem, "Doctrinal Deviations in Evangelical-Feminist Arguments about the Trinity," in Bruce A. Ware and John Starke, eds., One God in Three Persons: Unity of Essence, Distinction of Persons, Implications for Life [Crossway, 2015], chap. 1). Over the course of the essay, the author extensively criticized some of these approaches for subscribing to the doctrine of "inseparable operations." The doctrine of inseparable operations teaches that, because the three persons of the Trinity are one God, each person of the Trinity is operative in all of God's external works--from creation through redemption to consummation. More concisely stated: "the external works of the Trinity are indivisible" (opera trinitatis ad extra indivisa sunt). Though I share the author's complementarian commitments, as well as his concerns about the way some egalitarian theologians treat the Trinity, I believe his attempt to correct these treatments of the Trinity by denying the doctrine of inseparable operations represents a cure that is worse than the disease. To deny the doctrine of inseparable operations is to undermine classical trinitarian theology at its core.
As Lewis Ayres and others have demonstrated quite extensively over the past couple of decades, fourth century trinitarian thought, the context within which "Nicene Christianity" as we know it emerged, was characterized by three basic features: (1) a clear sense of the distinction between "person" and "nature" in the Godhead, with the understanding that there are three of the former and only one of the latter; (2) a conviction that the eternal generation of the Son does not constitute a division between the being of the Father and the being of the Son but rather that it occurs within the indivisible and incomprehensible being of God; and (3) a belief that the unity of being among the Father, the Son, and the Spirit entails a unity of operation in their works toward creatures. These three features, we should note, not only characterize fourth century trinitarian theology; they also characterize mainstream trinitarian theology East and West, late patristic, medieval, and modern, Catholic and Protestant.
The doctrine of inseparable operations has received broad acceptance in the church because it enjoys a solid foundation in Holy Scripture. The doctrine reflects a pattern of theological reasoning that follows from a biblical pattern of divine naming.
Consider just one example. In 1 Corinthians 8.6, Paul declares: "for us there is one God, the Father, from whom are all things and for whom we exist, and one Lord, Jesus Christ, through whom are all things and through whom we exist." In this text, the Apostle appropriates two common Jewish strategies, one drawn from the Old Testament, another borrowed from Greco-Roman God-talk, for affirming the absolute unity of God's identity and action. The language of "one God" and "one Lord" draws upon Deuteronomy 6.4 to affirm the unity of God's identity. The language about "all things" being "from" him and "through" him borrows discourse often used to describe the various "causes" of the universe in order to affirm that God alone is the supreme cause of all things--i.e., that all things are "from him and through him and to him," to quote Romans 11.36. The striking feature of 1 Corinthians 8.6 is that Paul locates the distinct identities of God the Father and the Lord Jesus Christ within the singular divine identity and within the singular divine causality that plans and accomplishes all things for God's glory. (For further discussion of this and other Pauline texts relevant to the doctrine of the Trinity, see Wes Hill's excellent book.)
This feature of the biblical naming of God constitutes the controlling grammar of the church's later trinitarian discourse. The distinction between divine persons is a distinction that obtains within the singular being of God without compromising or dividing that being. Similarly, the distinction between divine persons is a distinction that obtains within the singular agency of God without compromising or dividing that agency.
Of course, the flip side is true as well. The unity of God's being does not elide the distinction between the persons: The Father and the Son are one God and one Lord; but the Father is not the Son and the Son is not the Father. Furthermore, the unity of God's agency, as affirmed in the doctrine of inseparable operations, does not elide the distinction between the persons. Francis Turretin summarizes a broad ecclesiastical consensus on this point:
Although the external works [of the Trinity] are undivided and equally common to the single persons (both on the part of the principle and on the part of the accomplishment), yet they are distinguished by order and by terms. For the order of operating follows the order of subsisting. As therefore the Father is from himself, so he works from himself; as the Son is from the Father, so he works from the Father (here belong the words of Christ, 'the Son can do nothing of himself, but what he seeth the Father do,' Jn. 5:19). As the Holy Spirit is from both, so he works from both. They also differ in terms as often as any divine operation is terminated on any person. So the voice heard from heaven is terminated on the Father, incarnation on the Son and the appearance in the form of a dove on the Holy Spirit.
In other words, within the undivided action of God toward his creatures, the three persons act in accordance with their distinct identities: in every work of God outside of himself, the Father acts from himself, the Son acts from the Father, and the Spirit acts from the Father and the Son. The three act in an indivisible but not an indistinct manner. (This principle, by the way, constitutes the intratrinitarian basis of the Son's obedience to the Father in his incarnate state, as Mike Allen and I have argued here.)
The past twenty five years or so have not exactly been a golden age of evangelical reflection upon the Trinity. This is due in part to modern theological amnesia regarding some of the most basic elements of biblical, trinitarian reasoning (as Stephen Holmes has shown here). It is also due to the (all too often) haphazard manner in which the Trinity has been used in debates regarding gender roles in the church. Thankfully, things are slowly changing. As they do, both complementarians and egalitarians need to do some house cleaning in their theological polemics. Such house cleaning will require patience in recovering the categories of classical trinitarian theology and, more fundamentally, in recovering the patterns of biblical reasoning from which these categories derive and which, in turn, these categories serve to promote.
When engaging in theological polemics, we must be careful not to destroy the fruitful trees that may stand in the midst of our interlocutors' arguments (see Deut 20.19-20). Let's contend for a biblical understanding of gender and gender roles. But let's not compromise the doctrine of the Trinity in the process.