This book published by IVP Academic edited by Kelly M. Kapic is worth getting for Brannon Ellis’ paper alone titled, “Covenantal Union and Communion: Union with Christ as the Covenant of Grace.”
The paper deserves a careful read.
Kapic in the introduction provides an overview of Ellis’ chapter:
“Brannon Ellis hopes to enrich conversations between sanctification and justification by considering the place of union of Christ in sanctification, especially in terms of communion of the saints. Ellis argues that to be made new by Christ is inextricably bound to being “in” Christ, which in turn is inextricably bound to belonging to the church. In doing this, he does not collapse soteriology and ecclesiology into one another, but emphasizes the inseparability of the new covenant membership with the mystical union. In this respect, rather than seeing union with Christ as holding a particular place on the ordo salutis, it spans the ordo’s outworking of redemption from beginning to end.” (12)
Here is a brief quotation that I found helpful in the paper:
“The often-used biblical image of marriage also offers a compelling illustration of the basis of the application of redemption in the effectual, declaration of the basis of the application of redemption in the effectual, declarative speaking of God. The foundation for the marital union (actually becoming “one flesh”) is the announcement before God and those present, ‘I now pronounce you man and wife.’ It is awkward to say that the marriage union itself is the basis of the marriage’s legitimacy—in fact, union before pronouncement isn’t properly ‘martial’ at all! Being pronounced married is the legally legitimate context in which the one-flesh union takes root, and progresses from “just married” to “till death do us part.”* The human analogy obviously falls short in certain respects, but the suggestiveness of marriage as a figure for Christ’s relationship with the church in Ephesians 5:25-32 is significant, as well as the number of passages that speak of the church being Christ’s bride. So the nature of re-creation or “new creation” as a legally constituted relationship is an important context for understanding union with Christ, which, again, should not be taken in an individualistic sense—in a vitally personal sense, yet, but not an individualistic one.” (96-97)
*Ellis’ footnote: I am employing the typical language and forms of contemporary Western marriage in this example, but for the sake of this argument, the reality of marriage as a legally constituted covenant relationship (rather than a mutual ‘participation’ that thus ground its own legitimacy) is quite deeply rooted. See Ken Campbell, ed., Marriage and Family in the Biblical World (Downers Grove, IL: InterVarsity Press, 2003).