The book of Acts, Luke's second volume, begins with three promises, two given by Jesus himself and a third given on his behalf by two heavenly messengers. All three deserve a detailed consideration.
The first is "the promise of the Father, which [Jesus] said, 'you have heard from me; for John baptized with water, but you will be baptized with the Holy Spirit not many days from now.'"
Jesus tells his disciples to stay in the city a while longer. They are not yet equipped for the mission ahead. In a few short days, however, they will receive "the promise of the Father," the Holy Spirit poured out upon them, empowering them to proclaim the Gospel with accompanying signs and wonders. They will also be joined, in a few short days, by people from every nation under heaven. The feast of Pentecost will bring pilgrims from all over the world to Jerusalem. The disciples' first task will be to bear witness to the Risen Christ right there in Jerusalem, plating the seed in the hearts of people from all over the world.
The second promise involves the sending forth of the disciples to be "witnesses in Jerusalem and in all Judea and Samaria, and to the end of the earth." The Holy Spirit will not only empower the disciples for work in Jerusalem but, indeed for a mission that will carry them to the uttermost parts of the earth. God's true kingdom will not be limited geographically to Israel (as the disciples, at this point, still suppose), but will extend "to the end of the earth." As witnesses to the resurrection, the disciples will be the heralds of this coming kingdom that knows no national boundaries and has no end.
These first two promises Jesus makes to his disciples just before he is "lifted up and a cloud [takes] him out of their sight." The third and final promise will inspire the disciples with hope.
"And while they were gazing into heaven as he went," Luke writes, "behold, two men stood by them in white robes, and said, 'Men of Galilee, why do you stand looking into heaven? This Jesus, who was taken from you into heaven, will come in the same way as you saw him go into heaven.'"
This promise has a very practical significance that is often lost because of a lack of proper context. In what way did the disciples see Jesus "go into heaven?" It will not do simply to say they saw him go in a cloud and, therefore, he will come in a cloud. The ascension is only the final movement of drama that began when Jesus "set his fact to go to Jerusalem" (Luke 9:51). The events that take place from that time "until the day he was taken up" are described in detail by Luke, a careful historian, because he understands the whole drama of the journey to Jerusalem, the ordeal of Jesus' passion, death, and resurrection, to be that of Jesus being "taken up," glorified in the presence of the Father, vindicated through his suffering, and raised to glory on high at the right hand of the Father. It is in this way that the disciples saw "this Jesus" taken up from them into heaven. It is, likewise, in this way that these "men of Galilee" and all who believe because of their witness will see the promise of the Lord's coming fulfilled every time they remember, recount, and re-live "all that Jesus began to do and teach, until the day he was taken up."
The proper posture for a people waiting for the Lord's coming is not that of gazing off into the clouds or standing around "looking into heaven." The disciples were rebuked for doing that very thing. Rather, the proper posture for a people waiting for the coming of the Lord is the posture of perpetual worship, keeping ever before them the living memory of his passion, his death, his resurrection, and his ascension to the right hand of the Father. The promise of his coming, anticipated in worship, will be fulfilled in its completeness at the Last Day.