For I delivered to you as of first importance what I also received: that Christ died for our sins in accordance with the Scriptures, that he was buried, that he was raised on the third day in accordance with the Scriptures, and that he appeared to Cephas, then to the twelve.

 Three observations:

(1) Christ died for our sins on the cross forms the foundation for salvation of sinners. The entire Old Testament revealed this fundamental fact without which there would be and could be no redemption.
(2) He was buried, because he had died, proven by his three days in the grave. It was death that he defeated because the death of Christ was real and not a deception.
(3) The final fact of the gospel; "He rose again the third day according to the Scriptures." Of all the truths this is perhaps the greatest for the sinner to comprehend. With the resurrection we have the gospel; if the resurrection is denied, there is no hope - the gospel collapses.