v. 12 — The problem stated
Paul starts from what is proclaimed: Christ has been raised from the dead. He asks how some can also say there is no resurrection of the dead.
vv. 13–14 — First consequences
If there is no resurrection of the dead, then Christ has not been raised. If Christ has not been raised, preaching is void and their faith is void.
vv. 15–16 — Second consequences
The apostles would be false witnesses about God, because they testified that God raised Christ. The claim “the dead are not raised” again implies Christ is not raised.
vv. 17–19 — Final consequences
If Christ has not been raised, their faith is void, they remain “in” their sins, and those who have fallen asleep in Christ have perished. If hope in Christ is only for this life, believers are most to be pitied.