74 Luke next proceeds with his narrative in the following terms: “And as they thus spoke, Jesus Himself stood in the midst of them, and says unto them, Peace be unto you: it is I; be not afraid. But they were terrified and affrighted, and supposed that they had seen a spirit. And He said unto them, Why are you troubled? And why do thoughts arise in your hearts? Behold my hands and my feet, that it is I myself: handle me and see; for a spirit has not flesh and bones, as you see me have.
And when He had thus spoken, He showed them His hands and His feet.” It is to this act, by which the Lord showed Himself after His resurrection, that John is also understood to refer when he discourses as follows: “Then, when it was late on the first day of the week, and when the doors were shut where the disciples were assembled for fear of the Jews, came Jesus, and stood in the midst, and says unto them, Peace be unto you. And when He had so said, He showed unto them His hands and His side.” Thus, too, we may connect with these words of John certain matters which Luke reports, but which John Himself omits.
For Luke continues in these terms: “And while they yet believed not for joy, and wondered, He said unto them, Have ye here any meat? And they gave Him a piece of a broiled fish, and of an honeycomb. And when He had eaten before them, He took what remained, and gave it unto them.” Again, a passage which Luke omits, but which John presents, may next be connected with these words. It is to the following effect: “Then were the disciples glad when they saw the Lord. Then said Jesus to them again, Peace be unto you: as my Father has sent me, even so send I you.
And when He had said this, He breathed on them, and says unto them, Receive the Holy Ghost: Whose soever sins ye remit, they are remitted unto them; and whose soever sins ye retain, they are retained.” Once more, we may attach to the above section another which John has left out, but which Luke inserts. It runs thus: “And He said unto them, These are the words which I spoke unto you while I was yet with you, that all things must be fulfilled which were written in the law of Moses, and in the prophets, and in the Psalms, concerning me.
Then opened He their understanding, that they might understand the Scriptures, and said unto them, Thus it is written, and thus it behooved Christ to suffer, and to rise from the dead the third day: and that repentance and remission of sins should be preached in His name among all nations, beginning at Jerusalem. And you are witnesses of these things. And I send the promise of my Father upon you: but tarry ye in the city, until ye be endued with power from on high.” Observe, then, how Luke has here referred to that promise of the Holy Spirit which we do not elsewhere find made by the Lord, save in John's Gospel. And this deserves something more than a passing notice, in order that we may bear in mind how the evangelists attest each other's truth, even on subjects which some of them may not themselves record, but which they nevertheless know to have been reported.
After these matters, Luke passes over in silence all else that happened, and introduces nothing into his narrative beyond the occasion when Jesus ascended into heaven. And at the same time he appends this [statement of the ascension], just as if it followed immediately upon these words which the Lord spoke, at the same time with those other transactions on the first day of the week, that is to say, on the day on which the Lord rose again; whereas, in the Acts of the Apostles, the self-same Luke tells us that the event really took place on the fortieth day after His resurrection.
Finally, as regards the fact that John states that the Apostle Thomas was not present with these others on the occasion under review, whereas, according to Luke, the two disciples, of whom Cleophas was one, returned to Jerusalem, and found the eleven assembled and those who were with them, it admits of little doubt that we must suppose Thomas simply to have left the company before the Lord showed Himself to the brethren when they were talking in the terms noticed above.
Source: The Harmony of the Gospels (New Advent)