I Cor. 15:1 Moreover, brethren, I declare unto you the gospel which I preached unto you, which also ye have received, and wherein ye stand;
2. By which also ye are saved, if ye keep in memory what I preached unto you, unless ye have believed in vain.
3. For I delivered unto you first of all that which I also received, how that Christ died for our sins according to the scriptures;
4 And that he was buried, and that he rose again the third day according to the scriptures:
5. And that he was seen of Cephas, then of the twelve:
6. After that, he was seen of above five hundred brethren at once; of whom the greater part remain unto this present, but some are fallen asleep.
7. After that, he was seen of James; then of all the apostles
8. And last of all he was seen of me also, as of one born out of due time...
11. Therefore whether it were I or they, so we preach, and so ye believed.
That’s the essential heart of the gospel.