 In any case, there were people who did not believe in a resurrection. So here's Paul in 1 Corinthians 15 trying to straighten out the Corinthian church. He says in verse 3, I delivered to you first of all what I received, how Christ died for our sins according to the scriptures, and that he was buried, and that he rose again the third day according to the scriptures. Now, that's part of the gospel, folks. I don't know how you can be a Christian without it.