“WHICH ARE BAPTIZED FOR THE DEAD…” into Christ’s death - “Buried with him in baptism…” Col. 2:12 and Rom. 6:3
“IF THE DEAD RISE NOT AT ALL?…” then Christ would still be counted among the dead, vs.16
“WHY ARE THEY…” The doubters in verse 12
“THEN BAPTIZED FOR THE DEAD?” into Christ’s death, verse 17.
So the essence of Paul’s argument in verse 29 is: Your belief or unbelief in the resurrection is more than just an academic matter. It involves your very baptism into the fellowship of the Body of Christ. If you question the resurrection, you empty the sacrament of baptism of all its meaning both with respect to Christ and with respect to your own experience in Christ. But when you believe with Paul that “…Now is Christ risen from the dead and become the first fruits of them that slept…” (Vs. 20) then the sacrament of baptism becomes one of the most beautiful and meaningful of experiences.