Paul’s message from the very beginning had one main issue – resurrection from the dead. To the Jews he used resurrection as proof that Jesus was the Christ. He used resurrection when speaking to the Gentiles to prove that Jesus Christ is God.
Without resurrection there is no salvation, there is no hope, our faith is vain, and we are still dead in our sins.
1 Corinthians 15:16-19: For if the dead rise not, then is not Christ raised: And if Christ be not raised, your faith is vain; ye are yet in your sins. Then they also which are fallen asleep in Christ are perished. If in this life only we have hope in Christ, we are of all men most miserable.
Christ died and shed his blood as payment for the sins of the world, but if he never rose from the dead, it was all for naught. But, praise God:
1 Corinthians 15:20: But now is Christ risen from the dead, and become the firstfruits of them that slept.