Matthew Henry Commentary 1 Corinthians 15:12-19

"Now if Christ is preached that he hath been raised from the dead, how say some among you that there is no resurrection of the dead? But if there is no resurrection of the dead, neither hath Christ been raised: and if Christ hath not been raised, then is our preaching vain, your faith also is vain. Yea, we are found false witnesses of God; because we witnessed of God that he raised up Christ: whom he raised not up, if so be that the dead are not raised. For if the dead are not raised, neither hath Christ been raised: and if Christ hath not been raised, your faith is vain; ye are yet in your sins. Then they also that are fallen asleep in Christ have perished. If we have only hoped in Christ in this life, we are of all men most pitiable." — 1 Corinthians 15:12-19 (ASV)

Having shown that Christ was risen, the apostle answers those who said there would be no resurrection. There would have been no justification or salvation if Christ had not risen. And must not faith in Christ be vain, and of no use, if he is still among the dead?

The proof of the resurrection of the body is the resurrection of our Lord. Even those who died in the faith would have perished in their sins if Christ had not risen. All who believe in Christ have hope in him as a Redeemer; hope for redemption and salvation by him. But if there is no resurrection or future recompense, their hope in him can only be for this life.

And they must be in a worse condition than the rest of mankind, especially at the time and under the circumstances in which the apostles wrote, for then Christians were hated and persecuted by everyone. But it is not so; they, of all people, enjoy solid comforts amid all their difficulties and trials, even in the times of the sharpest persecution.