Objection 1. It would seem that Christ ought to have lived constantly with His Disciples, because He appeared to them after His Resurrection in order to confirm their faith in the Resurrection, and to bring them comfort in their disturbed state, according to John 20:20: "The disciples were glad when they saw the Lord." But they would have been more assured and consoled had He constantly shown them His presence. Therefore it seems that He ought to have lived constantly with them.
Objection 2. Further, Christ rising from the dead did not at once ascend to heaven, but after forty days, as is narrated in Acts 1:3. But meanwhile He could have been in no more suitable place than where the disciples were met together. Therefore it seems that He ought to have lived with them continually.
Objection 3. Further, as Augustine says (De Consens. Evang. iii), we read how Christ appeared five times on the very day of His Resurrection: first "to the women at the sepulchre; secondly to the same on the way from the sepulchre; thirdly to Peter; fourthly to the two disciples going to the town; fifthly to several of them in Jerusalem when Thomas was not present." Therefore it also seems that He ought to have appeared several times on the other days before the Ascension.
Objection 4. Further, our Lord had said to them before the Passion (Matthew 26:32): "But after I shall be risen again, I will go before you into Galilee"; moreover an angel and our Lord Himself repeated the same to the women after the Resurrection: nevertheless He was seen by them in Jerusalem on the very day of the Resurrection, as stated above (Objection 3); also on the eighth day, as we read in John 20:26. It seems, therefore, that He did not live with the disciples in a fitting way after the Resurrection.
On the contrary, It is written (John 20:26) that "after eight days" Christ appeared to the disciples. Therefore He did not live constantly with them.
I answer that, Concerning the Resurrection two things had to be manifested to the disciples, namely, the truth of the Resurrection, and the glory of Him who rose. Now in order to manifest the truth of the Resurrection, it sufficed for Him to appear several times before them, to speak familiarly to them, to eat and drink, and let them touch Him. But in order to manifest the glory of the risen Christ, He was not desirous of living with them constantly as He had done before, lest it might seem that He rose unto the same life as before. Hence (Luke 24:44) He said to them: "These are the words which I spoke to you, while I was yet with you." For He was there with them by His bodily presence, but hitherto He had been with them not merely by His bodily presence, but also in mortal semblance. Hence Bede in explaining those words of Luke, "while I was with you," says: "that is, while I was still in mortal flesh, in which you are yet: for He had then risen in the same flesh, but was not in the same state of mortality as they."
Reply to Objection 1. Christ's frequent appearing served to assure the disciples of the truth of the Resurrection; but continual intercourse might have led them into the error of believing that He had risen to the same life as was His before. Yet by His constant presence He promised them comfort in another life, according to John 16:22: "I will see you again, and your heart shall rejoice; and your joy no man shall take from you."
Reply to Objection 2. That Christ did not stay continually with the disciples was not because He deemed it more expedient for Him to be elsewhere: but because He judged it to be more suitable for the apostles' instruction that He should not abide continually with them, for the reason given above. But it is quite unknown in what places He was bodily present in the meantime, since Scripture is silent, and His dominion is in every place (Cf. Psalm 102:22).
Reply to Objection 3. He appeared oftener on the first day, because the disciples were to be admonished by many proofs to accept the faith in His Resurrection from the very out set: but after they had once accepted it, they had no further need of being instructed by so many apparitions. Accordingly one reads in the Gospel that after the first day He appeared again only five times. For, as Augustine says (De Consens. Evang. iii), after the first five apparitions "He came again a sixth time when Thomas saw Him; a seventh time was by the sea of Tiberias at the capture of the fishes; the eighth was on the mountain of Galilee, according to Matthew; the ninth occasion is expressed by Mark, 'at length when they were at table,' because no more were they going to eat with Him upon earth; the tenth was on the very day, when no longer upon the earth, but uplifted into the cloud, He was ascending into heaven. But, as John admits, not all things were written down. And He visited them frequently before He went up to heaven," in order to comfort them. Hence it is written (1 Corinthians 15:6-7) that "He was seen by more than five hundred brethren at once... after that He was seen by James"; of which apparitions no mention is made in the Gospels.
Reply to Objection 4. Chrysostom in explaining Matthew 26:32--"after I shall be risen again, I will go before you into Galilee," says (Hom. lxxxiii in Matth.), "He goes not to some far off region in order to appear to them, but among His own people, and in those very places" in which for the most part they had lived with Him; "in order that they might thereby believe that He who was crucified was the same as He who rose again." And on this account "He said that He would go into Galilee, that they might be delivered from fear of the Jews."
Consequently, as Ambrose says (Expos. in Luc.), "The Lord had sent word to the disciples that they were to see Him in Galilee; yet He showed Himself first to them when they were assembled together in the room out of fear. (Nor is there any breaking of a promise here, but rather a hastened fulfilling out of kindness)" [Cf. Catena Aurea in Luc. xxiv, 36]: "afterwards, however, when their minds were comforted, they went into Galilee. Nor is there any reason to prevent us from supposing that there were few in the room, and many more on the mountain." For, as Eusebius [Of Caesarea; Cf. Migne, P. G., xxii, 1003] says, "Two Evangelists, Luke and John, write that He appeared in Jerusalem to the eleven only; but the other two said that an angel and our Saviour commanded not merely the eleven, but all the disciples and brethren, to go into Galilee. Paul makes mention of them when he says (1 Corinthians 15:6): 'Then He appeared to more then five hundred brethren at once.'" The truer solution, however, is this, that while they were in hiding in Jerusalem He appeared to them at first in order to comfort them; but in Galilee it was not secretly, nor once or twice, that He made Himself known to them with great power, "showing Himself to them alive after His Passion, by many proofs," as Luke says (Acts 1:3). Or as Augustine writes (De Consens. Evang. iii): "What was said by the angel and by our Lord--that He would 'go before them into Galilee,' must be taken prophetically. For if we take Galilee as meaning 'a passing,' we must understand that they were going to pass from the people of Israel to the Gentiles, who would not believe in the preaching of the apostles unless He prepared the way for them in men's hearts: and this is signified by the words 'He shall go before you into Galilee.' But if by Galilee we understand 'revelation,' we are to understand this as applying to Him not in the form of a servant, but in that form wherein He is equal to the Father, and which He has promised to them that love Him. Although He has gone before us in this sense, He has not abandoned us."
Source: Summa Theologica (New Advent)