Most Christian theologians distinguish the (physical) union with Christ established at his incarnation from what Paul seems to highlight, namely, our participation in Jesus’ death and resurrection, that is, his redemptive work: “I have been crucified with Christ” (Gal. 2:20).
For Paul, the work of Christ does not establish a union with humanity in general but rather for a distinct group: “Christ loved the church and gave himself up for her” (Eph. 5:25). Those who place their faith in Christ share in Christ’s resurrection, the “first fruits” of a great end-time resurrection harvest (1 Cor. 15:20).
The “already” of believers’ being raised with Christ (Eph. 2:5; Col. 2:12–13; 3:1), and the bodily resurrection yet to come, and are but two episodes of one and the same event: Christ’s resurrection. Incorporation into Christ’s death and resurrection happens not at the believer’s birth (i.e., by virtue of being born human) but baptism (i.e., by virtue of saving faith): “Do you not know that all of us who have been baptised in Christ Jesus were baptised into his death?” (Rom. 6:3; cf. 6:4–5).
To be blessed in Christ in this context is to be incorporated not into his nature but into his history, and baptism is the graphic public exhibit of the actualisation of such incorporation. Baptism marks the moment in our history when we are incorporated into Jesus’ history.