1 Corinthians 15:5

And that he was seen of Cephas - Peter; See the note at John 1:42. The resurrection of Christ was A fact to be proved, like all other facts, by competent and credible witnesses. Paul, therefore, appeals to the witnesses who had attested, or who yet lived to attest, the truth of the resurrection of the Lord Jesus; and shows that it was not possible that so many witnesses should have been deceived. As this was not the first time in which the evidence had been stated to them, and as his purpose was merely to remind them of what they had heard and believed, he does not adduce all the witnesses to the event, but refers only to the more important ones. He does not, therefore, mention the woman to whom the Saviour first appeared, nor does he refer to all the times when the Lord Jesus manifested himself to his disciples. But he does not refer to them in general merely, but mentions “names,” and refers to persons who “were then alive,” who could attest the truth of the resurrection. It may be observed, also, that Paul observes probably the exact “order” in which the Lord Jesus appeared to the disciples, though he does not mention all the instances. For an account of the persons to whom the Lord Jesus appeared after his resurrection, and the order in which it was done, see the notes on the Gospels.

Then of the twelve - The apostles; still called “the twelve,” though Judas was not one of them. It was common to call the apostles “the twelve.” Jesus appeared to the apostles at one time in the absence of Thomas John 20:19, John 20:24; and also to them when Thomas was present, John 20:24. Probably Paul here refers to the latter occasion, when all the surviving apostles were present.