John Calvin Commentary 1 Corinthians 15:5

"and that he appeared to Cephas; then to the twelve;" — 1 Corinthians 15:5 (ASV)

That he was seen by Cephas. He now brings forward eye-witnesses, (αὐτόπτας), as they are called by Luke (Luke 1:2), who saw the accomplishment of what the Scriptures had foretold would take place. He does not, however, adduce them all, for he makes no mention of women. Therefore, when he says that he appeared first to Peter, you are to understand by this that he is put before all the men, so that there is nothing inconsistent with this in the statement of Mark (Mark 16:9) that he appeared to Mary.

But why does he say that he appeared to the twelve, when, after the death of Judas, there were only eleven remaining? Chrysostom is of the opinion that this took place after Matthias had been chosen in his place. Others have chosen rather to correct the expression, viewing it as a mistake. But as we know that there were twelve in number who were set apart by Christ’s appointment, though one of them had been expunged from the roll, there is no absurdity in supposing that the name was retained. On this principle, there was a body of men at Rome called the Centumviri, even though they actually numbered 102. By the twelve, therefore, you are simply to understand the chosen Apostles.

It is not entirely clear when this appearing to more than five hundred took place. It is possible, however, that this large multitude assembled at Jerusalem when he manifested himself to them. For Luke (Luke 24:33) mentions in a general way the disciples who had assembled with the eleven, but he does not say how many there were. Chrysostom refers this event to the ascension and explains the word ἐπάνω to mean, from on high. Unquestionably, regarding his appearance to James individually, this may have occurred after the ascension.

By all the Apostles I understand not merely the twelve, but also those disciples to whom Christ had assigned the office of preaching the gospel. Just as our Lord desired many witnesses of his resurrection and frequent testimony to it, let us also recognize that it should be all the more surely believed among us. (Luke 1:1). Furthermore, since the Apostle proves the resurrection of Christ from the fact that he appeared to many, he implies by this that it was not figurative but true and natural, for the eyes of the body cannot be witnesses of a spiritual resurrection.