Union with Christ
In its widest sense, the phrase union with Christ refers to the relationship between the believer and Jesus Christ. In this sense, John Murray says, union with Christ is "the central truth of the whole doctrine of salvation." The expression "in Christ" (en Christo, en kyrio, en Christo Iesou, en auto etc.) occurs 216 times in the Pauline letters and 26 times in the Johannine literature. Hence, according to Albert Schweitzer, "This 'being-in-Christ' is the prime enigma of the Pauline teaching: once grasped it gives the clue to the whole."  Given the large number of occurrences and the wide range of contexts, the phrase embodies a breadth of meaning. (For example; Paul uses the phrase "en Christo" as a synonym for a Christian (Romans 16:7) and the phrase "en emoi" to describe the intimate identification of Christ with the believer (Galatians 2:20).)
According to the narrower sense of the phrase, used in Christian theology, union with Christ is a step in the ordo salutis ("order of salvation"), and the basis of the believer's justification. In this sense, union with Christ follows faith and precedes adoption (Galatians 3:26-27). Augustus Strong describes it in this way: "union with Christ logically precedes both regeneration and justification; and yet, chronologically, the moment of our union with Christ is also the moment when we are regenerated and justified."
Historical interpretations 
Roman Catholic 
Traditional Roman Catholic theology centres the union with Christ in a substantial sense on the unity of the institutional church, past and present. "The communion of saints is the spiritual solidarity which binds together the faithful on earth, the souls in purgatory, and the saints in heaven in the organic unity of the same mystical body under Christ its head." Christians, according to Roman Catholic theology, are united to Christ through the sacraments.
In Reformed theology, union with Christ is understood to be a comprehensive category that runs through the entire doctrine of Salvation. John Murray observes; "Union with Christ is a very inclusive subject. It embraces the wide span of salvation from the ultimate source in the eternal election of God to its final fruition in the glorification of the elect."
As a step in the order of salvation, union with Christ was seen by John Calvin to be the basis for both justification and sanctification. Alister McGrath notes that while Martin Bucer suggested that justification causes (moral) regeneration, Calvin argued that "both justification and regeneration are the results of the believer's union with Christ through faith."
Some Evangelicals see union with Christ as a discrete stage in the "order of salvation." The evangelical theologian William Shedd comments "The impartation of Christ's righteousness presupposes a union with him." Robert Dabney while avoiding deification said that the bond of the union is the indwelling of the Holy Spirit.
Eastern Orthodox 
Eastern Orthodox theology emphasizes the incarnation as the starting point for our union with Christ. "In Christ God becomes one with us in order to make us one with him; he stooped to take our nature, in order that we might be restored to become partakers of his nature."
Theological Content 
In Christian theology the union of Christ is built on the a priori assumption of Adam's union with humanity (Romans 5:12-21). Also according to the Apostle Paul, Christ's death and resurrection is a prerequisite for believers to be identified with Christ (Romans 6:8-10). In other words the vicarious death of Jesus is the basis for incorporation into Christ.
The New Testament teaches that union with Christ is precipitated by faith and baptism, i.e. we believe and are baptized "into" Christ (John 3:16, Romans 6:3). Both the apostle John and Paul employ the Greek preposition eis rather than en in these passages to convey the notion of union with Christ. The ESV Study Bible explains the use of this particular preposition in its note on John 11:25, "The preposition translated “in” (Gk. eis) is striking, for eis ordinarily means “into,” giving the sense that genuine faith in Christ in a sense brings people “into” Christ, so that they rest in and become united with Christ. (This same expression is found in 3:16, 18, 36; 6:35; 7:38; 12:44, 46; 14:12; 1 John 5:10.)"
|“||I am the vine; you are the branches.
Whoever abides in me and I in him,
he it is that bears much fruit,
for apart from me you can do nothing.
—John 15:5, ESV
There are a number of ways of describing the nature of the union with Christ. Roman Catholic theology holds that believers actually imbibe the physical body and blood of Christ when they partake in the Eucharist. Reformed theology using the model of federal headship, where humanity is covenantally represented by Adam, sees Christians represented covenantally by Christ. Pietist theology see a union with Christ as mystical, "hidden" in the spiritual dimension. Evangelical theology contains the idea of an experiential union, where Jesus having gone through life, death and resurrection, shares these experiences with believers. Both Reformed and Evangelical theology acknowledges that union with Christ is the subjective application of God's objective work in Salvation. In Protestant theology the phrase union with Christ means a mutual indwelling (John 14-15), of Christians and the triune God, without affirming that Christians are absorbed into God. Several biblical themes are expressed within concept of being "in Christ." For example the Old Testament notion of God dwelling among the Israelites (Exodus 25:8) is expressed by Jesus in the New Testament as the triune God dwelling with believers (John 14:23).
- An organic union - in which believers become members of Christ and enjoy a mutual, reciprocal dependence on Christ for life and He on them for expression (Eph. 5:29-30).
- A vital union - in which Christ operates within believers as their life and becomes the dominating principle within them (Gal. 2:20; Col. 3:3-4).
- A spiritual union - that is, a union originating from and sustained by the Holy Spirit in their spirit (Rom. 8:9-10; Eph 3:16-17).
- An indissoluble union - that is, a union which, by virtue of Christ's eternal, divine, and incorruptible power and grace, can never be dissolved (Matt. 28:20; Rom. 8:39; Heb. 7:16).
- An inscrutable union - that is, a divine and mystical union of knowledge-surpassing intimacy and value (Eph. 3:19; 5:32; Col. 1:27).
The blessings of Salvation observes Philip Ryken are obtained by being "in Christ." Furthermore union with Christ has a relational dimension, because believers are brought into fellowship with the Trinity (John 17:21 and Romans 8:9). Being "in Christ" means for Christians being part of one body of believers (Romans 12:5).
- John Murray, Redemption : Accomplished and Applied (Grand Rapids: Eerdmans, 1955): 161.
- Bruce Demarest, The Cross and Salvation: The Doctrine of Salvation (Wheaton: Crossway Books, 1997): 313.
- Schweitzer, Albert. The Mysticism of Paul the Apostle. Baltimore: John Hopkins University Press, 1998, p. 3
- Demarest, The Cross and Salvation, 326.
- Philip Ryken, The Message of Salvation, BST (Leicester: Inter-Varsity Press, 2001): 186.
- Augustus Strong, 'Union With Christ' monergism.com. http://www.monergism.com/union_augustus.html Retrieved 24 May 2009.
- J. Sollier, 'The Communion of Saints' Catholic Encyclopedia. (New York: Robert Appleton Company, 1908) http://www.newadvent.org/cathen/04171a.htm Retrieved 20 May 2009.
- J.P. Baker 'Union with Christ,' New Dictionary of Theology (Downers Grove: IVP Academic, 1988): 698.
- Demarest, The Cross and Salvation, 319.
- As cited in Demarest, The Cross and Salvation, 320.
- Alister E. McGrath, Reformation Thought: An Introduction (3rd ed; Oxford: Blackwell, 1999): 125.
- Demarest, The Cross and Salvation, 323.
- As cited in Demarest, The Cross and Salvation, 324.
- Demarest, The Cross and Salvation, 325.
- Baker 'Union with Christ,' 698.
- Robert Letham, The Work of Christ (Downers Grove: InterVarsity Press, 1993): 82.
- Demarest, The Cross and Salvation, 329.
- Demarest, The Cross and Salvation, 330.
- English Standard Version Study Bible. Wheaton: Crossway, 2011. Print
- Pohle, 'Eucharist,' http://www.newadvent.org/cathen/05572c.htm Retrieved 21 May 2009.
- Baker, New Dictionary of Theology, 698.
- Baker, New Dictionary of Theology,' 699.
- Baker, New Dictionary of Theology,' 698.
- Michael Horton, 'Union with Christ' monergism.com. http://www.monergism.com/thethreshold/articles/questions/horton/union.html Retrieved 24 May 2009.
- Herman Ridderbos, 'Fundamental Structures: In Christ, With Christ' Paul: An Outline of His Theology. http://www.geftakysassembly.com/Articles/BiblicalExposition/InChristWithChrist.htm Retrieved 24 May 2009.
- ^ Strong, Augustus H. Systematic Theology. Valley Forge: Judson Press, 1907, p. 800-801
- Ryken, The Message of Salvation, 189.
- Wayne Grudem, Systematic Theology: An Introduction to Biblical Doctrine (Nottingham:IVP, 1994): 847.
- Grudem, Systematic Theology, 844.
- Bibliography of Resources on Union with Christ, by Phil Gons
- An Annotated Bibliography of Resources Pertaining to "Christ in You" and "Union with Christ", by James A. Fowler
See also 
- Imputed righteousness
- Justification (theology)
- Divinization (Christian)
- Theosis (Eastern Orthodox theology)