In Pauline thought, baptism is closely linked with union with Christ. We are baptized into union with the Lord. We are baptized into Jesus’ death and resurrection (Rom. 6.3; Col. 2.12). As we are baptized into union with Christ, we are adopted as “sons of God through faith,” and we become “Abraham’s offspring, heirs according the the promise.” (Gal. 3.26-29)
In fact, the way Paul speaks of baptism does not leave much room for suggesting that baptism is a “mere symbol” of union with Christ; rather, baptism actually effects that which it symbolizes. In Paul, the sign and the thing signified are not to be pulled apart. So, how do we make sense of this? How does baptism bring us into union with the risen Christ?
Paul’s answer is that baptism into Christ is baptism into the whole Christ, both head and body, what St. Augustine called the Totus Christus. Baptism is the doorway into the Church, the body of Christ:
“For just as the body is one and has many members, and all the members of the body, though many, are one body, so it is with Christ. For in one Spirit we were all baptized into one body…” (1 Cor. 12.12-13)
To be in the Church, the body of Christ, is to be in Christ. Thus baptism into the Church is baptism into union with Christ.