The Resurrection of Christ
Paul reminds them of the gospel he preached, which they received and in which they still stand. By this gospel they are being saved, provided they hold fast to the word he preached rather than having believed emptily.
N1ow, brothers, I want to remind you of the gospel I preached to you, which you received, and in which you stand firm. 2By this gospel you are saved, if you hold firmly to the word I preached to you. Otherwise, you have believed in vain.
Paul passes on what he himself received as first importance: that Christ died for sins according to the Scriptures, was buried, was raised on the third day according to the Scriptures, and appeared to Cephas, the Twelve, more than five hundred brothers, James, all the apostles, and finally to Paul himself. The resurrection is therefore not an isolated claim, but the heart of the message witnessed by many.
3For what I received I passed on to you as of first importance: that Christ died for our sins according to the Scriptures, 4that He was buried, that He was raised on the third day according to the Scriptures, 5and that He appeared to Cephas and then to the Twelve. 6After that, He appeared to more than five hundred brothers at once, most of whom are still living, though some have fallen asleep. 7Then He appeared to James, then to all the apostles. 8And last of all He appeared to me also, as to one of untimely birth.
Paul says he is the least of the apostles and unworthy because he once persecuted the church, yet by God's grace he is what he is, and that grace has been fruitful in him. Whether preached by Paul or by the others, the message is the same one the Corinthians believed.
9For I am the least of the apostles and am unworthy to be called an apostle, because I persecuted the church of God. 10But by the grace of God I am what I am, and His grace to me was not in vain. No, I worked harder than all of them — yet not I, but the grace of God that was with me. 11Whether, then, it was I or they, this is what we preach, and this is what you believed.