Charles Spurgeon Commentary 1 Corinthians 15:1-3

"Now I make known unto you brethren, the gospel which I preached unto you, which also ye received, wherein also ye stand, by which also ye are saved, if ye hold fast the word which I preached unto you, except ye believed in vain. For I delivered unto you first of all that which also I received: that Christ died for our sins according to the scriptures;" — 1 Corinthians 15:1-3 (ASV)

Which I preached to you, which also you have received, and in which you stand; by which also you are saved, if you keep in memory what I preached to you, unless you have believed in vain. For I delivered to you first of all that which I also received, that Christ died for our sins according to the scriptures;

That is the central truth of the gospel.