In the context of Pauline theology, what is the significance of the phrase 'in Christ' (ἐν Χριστῷ) regarding believers' union with Christ?

A It refers to a purely intellectual assent to Christian doctrine. B It signifies a mystical and transformative union whereby believers participate in Christ's life, death, and resurrection. C It indicates a superficial association with the Christian community. D It implies a future hope of being physically located in the same place as Christ.