How are Regeneration, Faith, and Union with Christ ordered in Reformed Theology? In the Reformed Ordo Salutis, or order of salvation, how are Regeneration, Faith, and Union with Christ ordered? (Note that the order of salvation is a logical order, not temporal, and the believer will experience several stages concurrently.)

Because of Total Depravity, the doctrine that we are spiritually dead in our sin, I think Regeneration is usually said to precede Faith, because we need to be brought back to spiritual life in order to have faith.

Faith is said to precede Union with Christ because it is through Faith that the Holy Spirit unites us the Christ.

But isn't it Union with Christ that gives us new life in Christ? Does Union with Christ therefore precede Regeneration? Or is the new life of Regeneration somehow different from the new life we receive through being united to Christ? How is this chicken-and-egg cycle resolved in Reformed Theology?
Union with Christ as a step within ordo salutis

The article The Puritans on Union with Christ, Justification, and Regeneration describes English Puritan Thomas Goodwin (1600-1680)'s solution to the "chicken and egg" problem based on his work The Object and Act of Justifying Faith by splitting the Union of Christ into two phases: 


before regeneration (not conscious) 
after regeneration when the sinner exercises their faith (conscious)


Quotes from the section "Union with Christ and the Ordo Salutis" (emphasis is mine)


  ... the common Reformed view on the order of justification and regeneration is that the latter precedes the former. But what about the role of union with Christ in relation to regeneration and justification?  ... But in relation to regeneration or, more specifically, effectual calling, Goodwin argues that union with Christ precedes regeneration. Christ first “apprehends” the believer: [quote from Goodwin].  This statement appears to indicate that union with Christ logically (not chronologically), precedes not only justification—a typical Reformed view—but even regeneration (narrowly considered).
  
  What makes Goodwin’s views on this matter perplexing is the fact that within the space of six pages he affirms there is a“threefold union with Christ”¹⁹ and a “twofold union with Christ.”²⁰ The first union is a relational union, like the union between a husband and wife. “And this union is fully and completely done when first we are turned to God, and when Christ takes us.”²¹ The second union involves the dwelling of Christ in the human body (Eph. 3:17)—“an actual inbeing of his person.” The third is objective, that is, having Christ as an object of faith “as the faculty doth view an object.”²² When Goodwin later speaks of the twofold union, he has in mind the first two under the heading of a “substantial union and communicative union.”²³ The union that we are especially concerned with is the first union, the union whereby the sinner is married to Christ. How does this happen? Returning to Goodwin’s comment above that “Christ takes me, and then gives me his Spirit, faith, holiness, &amp;c.,” we are faced with the question of whether union with Christ precedes faith itself.
  
  Goodwin’s The Object and Act of Justifying Faith is helpful in answering this question. In it, he speaks of the act of the will completing the union between Christ and the believer, which makes believers “ultimately one with him.”²⁴ However, as the bride, we are simply confirming the union that has taken place. So, contrary to the common view of marriage, which requires the consent of both partners since a man cannot marry a woman against her will, there is a spiritual union on Christ’s part to the elect that does not require assent from the sinner “because it is a secret work done by his Spirit, who doth first apprehend us ere we apprehend him.”²⁵ That is to say, Christ establishes a union with the elect sinner by“apprehending” him and then giving the Spirit to him. But this union is only complete (“ultimate union”) when the sinner exercises faith in Christ. This basic pattern is confirmed later in Goodwin’s work on justifying faith:
  
  
    It is true indeed the union on Christ’s part is in order of nature first made by the Spirit; therefore Philip. iii. 12, he is said first to “comprehend us ere we can comprehend him;” yet that which makes the union on our part is faith, whereby we embrace and cleave to him…. It is faith alone that doth it. Love indeed makes us cleave to him also, but yet faith first.²⁶
  
  
  Goodwin is at his finest when he speaks of Christ “taking,” “apprehending,” and “comprehending” the sinner. Christ “takes hold of us before we believe” and “works a thousand and a thousand operations in our souls to which our faith concurs nothing…. Christ dwells in us and works in us, when we act not and know not our union, nor that it is he that works.”²⁷ Before the new believer is aware, our Lord unites us to Himself (“takes hold of us”) and works in us. The Spirit then regenerates the sinner, who in turn exercises faith toward Christ and completes the union. From that union flow all other spiritual blessings.


Union with Christ as taking place throughout ordo salutis

Another way to solve the problem is by conceiving "Union with Christ" as taking place throughout ordo salutis, not simply as a step.  The 2 resources below explain this approach:


2011 book Union with Christ: In Scripture, History, and Theology by Dr. Robert Letham, Professor of Systematic and Historical Theology
LTh paper Ordo Salutis and Union with Christ by Sammy Davies, Jr., pastor of Ammanford Evangelical Church.


In the book, Dr. Letham spreads the interrelationship discussion in separate chapters: regeneration, faith, justification in Chapter 4; sanctification, adoption, and glorification in Chapter 5; death and resurrection in Chapter 6.  "The fact that union with Christ is paramount, far from requiring that we dispense with the ordo salutis, preserves and enhances it by pointing to its integrating feature."  He then noted that 


  The divines at Westminster knew this in the seventeenth century when they combined a logical or orderly ordo salutis in WCF 9-18 with the same topics considered as aspects of union and communion with Christ in grace and glory in WLC 65-90.  Moreover, it is at least open to question whether we are simply to follow precisely the same pattern as Paul did.  He was not the only biblical author.


Both references a 2006 book Richard B. Gaffin Jr. (but not recommend his solution): By Faith, Not by Sight: Paul and the Order of Salvation.  Mr. Davies noted that Gaffin "suggests that justification and sanctification are simply manifestations of union."  Quote from Letham:


  He has cautiously suggested the possibility that [order salutis] needed recasting.  This is in view of Paul's insistence that the center of the biblical revelation of salvation is the death and resurrection of Christ.  Our union with him in those epochal events, viewed in the eschatological sense that Paul gives them, should shape our soteriology, Gaffin suggests.  Gaffin has not intended to undermine the doctrine of justification only by faith, but rather to see the order of salvation in a manner compatible with the Pauline view of redemptive history.  Others, influenced by Gaffin, have voiced similar proposals.


Both Dr. Letham and Mr. Davies defended to preserve ordo salutis, the latter relying on another of Dr. Letham's 1993 book The Work of Christ - Contours of Christian Theology.  

After noting that Union with Christ in its simplest form is the joining of Christ and His Church, Mr. Davies helpfully analyzed "5 broad ways in which the Bible describes this union": 


Incarnational Union ("In becoming man Christ united Himself with the human race")
Covenantal Union (Hosea, Ephesian 5)
Sacramental Union (baptism, communion)
Experiential Union (Holy Spirit transforming believers into the likeness of Christ)
Mystical/Spiritual Union (Holy Spirit indwells all believers)


Mr. Davies's paper closes with 3 options / perspectives to relate Union with Christ and ordo salutis, recommending the last one (Letham's scheme) as the best option:


  
  Salvation can be viewed purely in light of the ordo salutis and as we have seen this has historically been the case in Reformed theology. It is not so much that union with Christ is considered an incorrect motif, but rather that it is neglected in favour of the rational, logically arranged, enlightenment endorsing ordo salutis simply substituted to mean effectual calling.
  
  
  [This is the relationship understood in the historical Reformed Church, see Andrew McGowan's 2004 paper "Justification and the ordo salutis"]
  
  
  The exact opposite of the first position could be adopted. Salvation could be seen as solely union with Christ. Union with Christ becomes a synonym for salvation and a strict ordo salutis is abandoned. Within this framework the different stages of the ordo are simply ‘benefits’ of the union rather than discrete acts. The aspects of the ordo are a direct result of being united to Christ. They are, all at once, terms which can immediately be associated with a believer by virtue of being in Christ. Gaffin suggests that justification and sanctification are simply manifestations of union.
  
  
  [This is the view of the Neo-Orthodox such as Barth or Hart]
  
  
  The third stance is to understand the ordo as taking place within the union. It is almost as if union with Christ is introduce as a new stage in the ordo salutis, but is perhaps better thought of as, “the dominant motif in any formulation of the application of redemption and dominate feature of any “order” of salvation.” The ordo salutis takes place in union much like a fish resides within water.
  
  Robert Letham expresses this understanding of union with Christ as “the foundation of all the blessings of salvation. Justification, sanctification, adoption and glorification are all received through our being united to Christ.”
  
  Furthermore, “The whole process of the application of salvation to us by the Holy Sprit (what has been known as ordo salutis – the order of salvation) fits in here as part of what it means to be united with Jesus Christ.” Essentially union with Christ isn’t actualised until the Holy Spirit works faith and repentance in a believer.
  
  
  [This is the view of those from the Westminster Theological Seminary stream.  Quotations from Letham's "The Work of Christ"]


Conclusion (from Mr. Davies's paper)


  The Bible is clear that in salvation there are different aspects even if they are received by the believer or take place at one and the same time. Terms such as justification, glorification, regeneration must be maintained as they are Biblical terms, which teach Biblical truths about the believer and the salvation they receive through the work of Christ and the Holy Spirit. Some sort of understanding of an ordo must be preserved therefore in order to reflect the instances in Scripture where such a progression is implied. Additionally the importance of having clearly defined and understood terms to express our salvation is indescribable and a loss of such terms would be detrimental to the Church. Without such terms confusion would reign over the role of God and man in salvation as well as the various benefits and ends to which it is designed.
  
  The Bible is equally as clear with regards the union of a believer with Christ as a major facet of salvation. To continue to ignore this in the way that reformed history has tended to do would be to read the Bible with only one eye open.
  
  As with many major themes in Scripture there is a healthy tension which must be maintained. The third perspective seems to maintain this tension more favorably than the other two as it seeks to describe the ordo salutis within a framework of union. Additionally this seems to be the method employed by Paul in both his letters to the Church in Rome and Ephesus.
  
  ...