Why could the Gospel go to the whole human race only after Jesus' death and resurrection?

Les explains that Jesus used the picture of a seed falling into the ground and dying to bring forth much fruit, referring to His coming death, burial, and resurrection, which were only a few days in the future. He stresses that Christ in His earthly ministry was almost exclusively to the nation of Israel, with only two exceptions. For Gentiles, He was not an object of their faith until He had experienced the work of the cross. But after His death, burial, and resurrection, the Gospel could go to the whole human race, not just Israel, because He then became the object of faith for the whole human race. Les also connects this to I Corinthians 15, where the resurrection of the dead is compared to planting a seed: the body is sown in corruption and raised in power. Paul was led by the Holy Spirit to make much of resurrection because when Christ arose, He exhibited more power than it took to create the universe.