This is my initial bibliography for studying Paul’s use of “in Christ” – see Summer Blogging. Some I have read before and have included some basic thoughts in parentheses. I would appreciate your feedback on who is missing, who has been helpful to you in studying the phrase:
1. Adolf Deissmann (Christ-intimacy – communion not union)
2. Wilhelm Bousset (comprehensive fellowship – spiritual relationship with exalted Lord)
3. Albert Schweitzer (Christ-mysticism; fellowship with God mediated through mystical union w/ Christ)
4. John Murray (union with Christ – Christ dwells in his people and his people dwell in him)
5. Karl Barth – (participation [objective] in Christ – human nature does not exist apart from its being in Christ; union [subjective] with Christ – realised only through obedience)
6. E.P. Sanders – (participation – by sharing in Christ’s death one dies to power of sin thus belonging to God; a present reality)
7. Michael Gorman – (theosis – like God; transformative participation in the kenotic, cruciform character of God through Spirit-enabled conformity to the incarnate, crucified, and resurrected/glorified Christ)
8. Con Campbell – (reading now)
Others to Consider: James Dunn, Tom Wright, Richard Hays, Douglas Campbell, Susan Eastman, Lou Martyn, John Barclay, Beverly Gaventa, Bruce Longenecker, Ben Blackwell, Tom Schreiner, Doug Moo…
Cruciform Theology 
I know this is an old post, but in case others come across it, I’ve been reading through another interesting contribution: Emmanuel Rehfeld, Relationale Ontologie bei Paulus
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Any discussion on Paul’s basic understanding, belief and his preaching gospel to the jews and gentiles, must take into consideration the earlier treatment of paul’s mysticism, and his contemporary theologians of his life time. Pauline mysticism has been greatly discussed in Scweitzer’s book, Paul’s mysticism of jesus.
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