'And if Christ has not been raised, then is our preaching vain, your faith also is vain.'
The whole of the Apostolic teaching was based on the fact that Jesus Christ had died, been buried and had risen again. The resurrection was not only the source of their faith in the effectiveness of what He had done, but was itself also the evidence of God's acceptance of it. And it was the spur that drove them on. It was as it were their trump card. Without that they had no message. Without that the Master was dead, and there was no avoiding the fact. Glorious though His teaching was, without the resurrection it was just another addition to the wisdom of the ages, even if a unique one. It was the fact that Christ had risen that had brought men new hope. It was that that had made the Apostles certain about the future, and confident that He was what He had said He was, the Lord of glory. It was that that had demonstrated that He had been declared both Lord and Christ (Acts 2:36).
A living on of the soul would have proved nothing except that the soul could live on, and how could they ever have known that it was true? But the resurrection of the body, after His giving of Himself up to death, had made all the difference. It had revealed that He had been right in all He had said, it had declared the success of Christ's sacrifice of Himself on the cross, it had demonstrated the defeat of death, and it had shown God's full satisfaction with what He had accomplished. It was moreover also a pointer to the coming redemption of all things. So without that the Apostolic preaching was but a vanity, a nothing, and if that was so it meant that the faith of the Corinthians was also useless and nothing and empty. They had accepted an invalid message.