1 Corinthians 15:5 - Matthew Poole's English Annotations on the Holy Bible

We read not in the history of the gospel of Christ's appearing unto Peter, unless he were one of those to whom Christ appeared, as they were going to Emmaus; for which there is this probability, because when they came to Jerusalem, they told the rest, that the Lord was risen, and had appeared unto Simon, Luke 24:34 (if Simon Peter be there meant). His appearance to the whole number of the disciples we have recorded, 1 Thessalonians 20:19: they are called twelve, (though Judas was now dead, and Thomas at that time was not there), because twelve was the number that God had appointed the college of apostles to consist of; so, Genesis 42:13, the children of Jacob said they were twelve brethren, though they thought at that time that Joseph (who made the twelfth) was dead. This is much more probably the sense, than the fancy of some, that Barnabas, who was afterward chosen to supply the room of Judas, being at that time a disciple, might at that time be with them; for admit he were, yet Thomas, we are sure, was at that time absent.