Why does Paul emphasize the resurrection so much?
Paul emphasizes the resurrection because Christ's rising from the dead displayed greater power than the power required to create the universe. After His death, burial, and resurrection, He becomes the object of faith for the whole human race, not just Israel.
Les teaches that Paul was led of the Holy Spirit to make so much of resurrection because when Christ arose from the dead, He exhibited more power than it took when He created the universe. In the surrounding context, Les explains that Christ in His earthly ministry was almost exclusively to the nation of Israel. But after experiencing the death, burial, and resurrection, the Gospel can go to the whole human race, not just Israel. Once He has died, been buried, and raised from the dead, He becomes the object of faith for the whole human race. This is tied to the seed principle: unless it dies, it cannot bring forth much fruit, pointing to His coming death, burial, and resurrection.