See e.g. Michael Horton, The Christian Faith: A Systematic for Pilgrims On the Way (Grand Rapids: Zondervan, 2011), 590.
 See 2 Cor. 5:17 “in Christ” (ἐν Χριστῷ), v. 18 “through Christ” (διὰ Χριστοῦ), v. 19 “in Christ” (ἐν Χριστῷ, v. 21 “in Him” (ἐν αὐτῷ).
 See e.g. 1 Cor. 15:24-28; Col. 1:15-20.
 “The resurrection of Christ in fact means the breakthrough of the new aeon in the real, redemptive-historical sense of the word, and therefore cannot be understood only in forensic, ethical, or existential categories. This all-embracing significance of the resurrection of Christ is in Paul likewise not only the fruit of his profound theological reflection, but about all of divine revelation. For, as he himself expresses it, when it pleased God to reveal his Son to him (Gal. 1:15), that was first and foremost the evidence for him that Jesus of Nazareth, who was crucified and had died and whom he himself had persecuted, was the Son of God and the Messiah of Israel. And it was this certainty, entirely foreign and even offensive to Jewish thinking, which determined his insight into the redemptive-historical significance of Christ’s death and resurrection in a decisive manner. Because Jesus was the Christ, his resurrection is not, as previous raisings of the dead, an isolated occurrence, but in it the time of salvation promised in him, the new creation, dawns in an overwhelming manner, as a decisive transition from the old to the new world (2 Cor. 5:17; cf. v. 15)” (Herman N. Ridderbos, Paul: An Outline of His Theology trans. John Richard De Witt [Grand Rapids: Wm. B. Eerdmans Publishing Co., 1975], 55-56).
 “The expression ‘in Christ’ is one of Paul’s most characteristic formulations and its precise meaning has been vigorously debated” (George Eldon Ladd, A Theology of the New Testament [Grand Rapids, William B. Eerdmans Publishing Co., 1993], 523). Union with Christ is often referred to as “mystical union” because union with Christ encompasses so much and is hard to define. A. A. Hodge says it is designated “mystical” because it “transcends all the analogies of earthly relationship, in the intimacy of its communion, in the transforming power of its influence, and in the excellence of its consequence” (Horton, The Christian Faith, 590 see also “Defining ‘Union with Christ,’ 406-20 in Constantine R. Campbell’s Paul and Union with Christ: An Exegetical and Theological Study [Grand Rapids: Zondervan, 2012).
 Philip Edgcumbe Hughes, Paul’s Second Epistle to the Corinthians (Grand Rapids: Wm. Bible Eerdmans Publishing Co., 1962), 202. See also John Calvin, Institutes, 2.16.19.
 B. Witherington III, “Christ” in Dictionary of Paul and His Letters, ed. Gerald F. Hawthorne, Ralph P. Martin, and Daniel G. Reid (Downers Grove: InterVarsity Press, 1993), 98.
 John Murray, Redemption Accomplished and Applied (Grand Rapids: Wm. B. Eerdmans Publishing Co., 1955), 161. “As far back as we can go in tracing salvation to its fountain we find ‘union with Christ’; it is not something tacked on; it is there from the outset” (Ibid., 162). “Communion with God is the crown and apex of true religion” (Ibid., 170). “Union with Christ is the central truth of the whole doctrine of salvation” (Ibid.).
 Robert A. Peterson, Salvation Applied by the Spirit: Union with Christ (Wheaton: Crossway, 2015), 19.
 Peterson, Salvation Applied by the Spirit, 20. Truly, “to be biblical we must first do justice to the Old Testament context, and in the case of typology we must discern whether something is a legitimate type/pattern. Then we must think through that pattern’s intertextual development across the biblical covenants, and then finally ask how it is brought to fulfillment in Christ and the arrival of the new covenant age” (Peter J. Gentry and Stephen J. Wellum, Kingdom through Covenant: A Biblical-Theological Understanding of the Covenants [Wheaton: Crossway, 2012], 607).
 See Peterson, Salvation Applied by the Spirit, 20-32 see also Campbell, Paul and Union with Christ, 406-20. In my reading, Cambell has given the fullest explanation and definition of what it means to be “in Christ.”
 Campbell, Paul and Union with Christ, 420.
 I was helped by Richard M. Davidson’s working paper “Corporate Solidarity in the Old Testament” (http://www.gospelstudygroup.org/wp-content/uploads/2010/08/corporate-solidarity-in-OT.pdf). Richard M. Davidson is J. N. Andrews Professor of Old Testament Interpretation at Andrews University.
 Though it should be understood that not everyone accepts this idea of federal headship. See e.g. J.W. Rogerson, “The Hebrew Conception of Corporate Personality: A Re-examination” in JTS 21 (1970) and Andrew Perriman, “The Corporate Christ: Re-assessing the Jewish Background” in Tyndale Bulletin 50.2 (1999) 239-63.
 “For Paul, all humankind is automatically ‘in Adam’, it would appear that the state of being ‘in Christ’ is brought about through the faith and baptism of individuals (Gal 3.26-28)” (Margaret E. Thrall, The Second Epistle to the Corinthians [Edinburgh, Scotland: T&T Clark, 1994], 410).
 Of course, one of the differences was that none of those animals rose victoriously out of the grave. None of the animals conquered death. None of the animals inaugurated the new creation.
 “From creation to the flood to the exodus all the way to the new creation, there is a close connection between the covenant and union with the covenant mediator” (Horton, The Christian Faith, 589).
 It seems also that marriage language is perhaps a foreshadowing. Husband and wife certainly have union and Israel is said in various places to be God’s bride, even if unfaithful (cf. Hosea). Of course, this is an example of a type of anthropomorphic language but we perhaps see precedence for union with Christ here too. Paul may be making this equation when he talks about the Church being the bride of Christ.
 See Peterson, Salvation Applied by the Spirit, 234-48.
 “In the case of both Adam and Christ, one action has had consequences of universal significance” (Philip Edgcumbe Hughes, Paul’s Second Epistle to the Corinthians [Grand Rapids: Wm. B. Eerdmans Publishing Co., 1962], 195)
 “The idea that the destinies of the Messiah and the people of God are linked is not unique (e.g. Dan. 7:9-27; 2 Baruch 30)” (M. A. Seifrid, “In Christ” in Dictionary of Paul and His Letters ed. Gerald F. Hawthorne, Ralph P. Martin, and Daniel G. Reid (Downers Grove: InterVarsity Press, 1993), 435).