85 Let us therefore compare what is said by the Apostle Paul with the view of deciding whether it raises any question of difficulty. His statement proceeds thus: “That He rose again the third day according to the Scriptures, and that He was seen of Cephas.” He does not say, “He was seen first of Cephas.” For this would be inconsistent with the fact that it is recorded in the Gospel that He appeared first to the women. He continues thus: “then of the twelve;” and whoever the individuals may have been to whom He then showed Himself, and whatever the precise hour, this was at least on the very day of His resurrection.
Again he goes on: “After that He was seen of above five hundred brethren at once.” And whether these were gathered together with the eleven when the doors were shut for fear of the Jews, and when Jesus came to them after Thomas had gone out from the company, or whether the reference is to some other appearance subsequent to these eight days, no discrepancy is created. Again he says, “after that He was seen of James.” We ought not, however, to suppose this to mean that this was the first occasion on which He was seen of James; but we may take it to allude to some special appearance to that apostle by himself.
Next he adds, “then of all the apostles,” which does not imply that this was the first time that He showed Himself to them, but that from this period He lived in more familiar intercourse with them on to the day of His ascension. Finally he says, “And last of all He was seen of me also, as of one born out of due time.” But that was a revelation of Himself from heaven some considerable time after His ascension.
Source: The Harmony of the Gospels (New Advent)