Paul immediately indicated that his intention was to remind the Corinthians of the gospel he had preached to them. He did not rehearse the content of that gospel until verses 3-5 where He gave four components of the gospel, each introduced by the word “that.” These should be seen in two pairs. The first component in each pair is the most important (that Christ died and that He was raised). The second component confirms the first statement in each pair (that He was buried and that He was seen or appeared). Paul grounded the gospel of Jesus Christ in the Old Testament Scriptures.
He spends more time “confirming” the resurrection by citing many who had seen Jesus after the resurrection because some in the church at Corinth were saying that there was no resurrection of the dead (vs. 12).
In this passage (1 Corinthians 15:1-11), Paul reminded the Corinthians of the gospel of Christ, which is Christ’s death for sins and His resurrection from the dead, and urged them to continue believing it.