Some have wondered: Why this order? Why start in Jerusalem and work out from there? The primary reason was certainly that the most devout portion of the Jewish people--that portion who had been the most influenced by the preparatory preaching of John and Jesus--was always gathered at the great annual festivals (like Pentecost), and hence the most successful beginning could be made there.
"Now when He had spoken these things, while they watched, He was taken up, and a cloud received Him out of their sight. And while they looked steadfastly toward heaven as He went up, behold, two men stood by them in white apparel, who also said, 'Men of Galilee, why do you stand gazing up into heaven? This same Jesus, who was taken up from you into heaven, will so come in like manner as you saw Him go into heaven" (Acts 1:9-11).
It must have been exciting to witness Jesus ascending into a cloud and out of sight! It is reasonable to conclude that the "two men" in white apparel that Luke speaks of here were actually angels (cf. Luke 24:4 with John 20:12). As the apostles watched, apparently dumbfounded, the angels informed them that Jesus would come again "in like manner." In other words, Jesus' second coming--which has yet to take place--would involve Him coming from the clouds visibly in some sort of bodily form with angels present (cf. Matt. 25:31; I Thess. 4:16,17; II Thess. 1:7; Rev. 1:7).
But why did Jesus return to heaven at this time? There are several purposes that are known:
"Then they returned to Jerusalem from the mount called Olivet, which is near Jerusalem, a Sabbath day's journey. And when they had entered, they went up into the upper room where they were staying: Peter, James, John, and Andrew; Philip and Thomas; Bartholomew and Matthew; James the son of Alphaeus and Simon the Zealot; and Judas the son of James. These all continued with one accord in prayer and supplication, with the women and Mary, the mother of Jesus, and with His brothers" (Acts 1:12-14).
After Christ's ascension on Mt. Olivet, the apostles returned to Jerusalem (approximately three-fourths of a mile) as instructed. They gather in an upper room. Although we cannot know for certain, it seems likely that this was the same upper room that Jesus had used on His last night with them before His betrayal (cf. Luke 22:12). Only eleven apostles are named here since Judas Iscariot had committed suicide after betraying the Christ. These apostles waited in Jerusalem united and prayerful (cf. Luke 24:53) with certain women (including Jesus' mother) as well as the very half-brothers of Jesus (cf. Matt. 13:55)!