For since death came through a man, the resurrection of the dead comes also through a man

 1 Corinthians 15:1-28

By this gospel you are saved, if you hold firmly to the word I preached to you. Otherwise, you have believed in vain.

For what I received I passed on to you as of first importance: that Christ died for our sins according to the Scriptures, that he was buried, that he was raised on the third day according to the Scriptures, and that he appeared to Cephas, and then to the Twelve.

But by the grace of God I am what I am, and his grace to me was not without effect. No, I worked harder than all of them—yet not I, but the grace of God that was with me. Whether, then, it is I or they, this is what we preach, and this is what you believed.

And if Christ has not been raised, our preaching is useless and so is your faith.

But Christ has indeed been raised from the dead, the firstfruits of those who have fallen asleep. For since death came through a man, the resurrection of the dead comes also through a man.

The last enemy to be destroyed is death. For he “has put everything under his feet.

Why?

We trust that Jesus raised from the dead, Jesus conquered death, so we have hope, and we believe Jesus is our savior.

Paul witnessed the living God, Jesus, and the grace of God that was with him. So Paul preached the Gospel, even facing the danger to his life.

How?

I trust in the Lord and believe that Jesus rose from the dead; one day, I will rise from the dead with Jesus Christ.