1 The former treatise have I made, O Theophilus, of all that Jesus began both to do and teach,
2 Until the day in which he was taken up, after that he through the Holy Ghost had given commandments unto the apostles whom he had chosen:
3 To whom also he shewed himself alive after his passion by many infallible proofs, being seen of them forty days, and speaking of the things pertaining to the kingdom of God:
4 And, being assembled together with them, commanded them that they should not depart from Jerusalem, but wait for the promise of the Father, which, saith he, ye have heard of me.
5 For John truly baptized with water; but ye shall be baptized with the Holy Ghost not many days hence.
6 When they therefore were come together, they asked of him, saying, Lord, wilt thou at this time restore again the kingdom to Israel?
7 And he said unto them, It is not for you to know the times or the seasons, which the Father hath put in his own power.
8 But ye shall receive power, after that the Holy Ghost is come upon you: and ye shall be witnesses unto me both in Jerusalem, and in all Judaea, and in Samaria, and unto the uttermost part of the earth.
9 And when he had spoken these things, while they beheld, he was taken up; and a cloud received him out of their sight.
10 And while they looked stedfastly toward heaven as he went up, behold, two men stood by them in white apparel;
11 Which also said, Ye men of Galilee, why stand ye gazing up into heaven? this same Jesus, which is taken up from you into heaven, shall so come in like manner as ye have seen him go into heaven.
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The Savior's earthly ministry ends with His ascension. To an outside observer it may appear that He is simply leaving, disappearing into the shining cloud of God's presence. Leaving for some distant place where He can no longer be seen. Yet He is going where the King of that Kingdom must be, the Kingdom destined very soon to enter the world and begin its victorious procession.
On the day of His ascension, Jesus does precisely what His apostles ask Him about: He begins to build the Kingdom. To create it. True, His disciples still understand nothing as before: they still hope that the Kingdom will be earthly, that now at last it will become visible to everyone, and that their Teacher will finally be recognized as the Messiah, the King of this Kingdom. They are still waiting for miracles from this world.
Jesus, however, explains nothing to them. He only says to them: do not hurry. The times and seasons connected with the establishment of the Kingdom are not your concern. This is not a human matter at all; all times are in the Father's authority. But you, Jesus says to the disciples, wait for your hour. Wait for the Holy Spirit. Wait until God's breath breaks into your life and transforms it. Then you will understand everything. The meaning of Jesus' words is clear: until you become part of the spiritual process that began with the Savior's appearance in the world, you will not see the Kingdom. And even Him, the King of this Kingdom, you will not truly see without sharing in God's breath.
In essence, He is not going away at all. He is simply setting out for the place where a king must be when decisive events begin in his kingdom: to the throne, to the throne room, just as at a decisive moment a captain goes to the bridge or an army commander to his command post.
Before, while communicating with the apostles, He remained all the time at the very border of the Kingdom, the border that separates it from the world not yet transformed. Now He is moving from the border of the Kingdom into its depths. This, of course, does not mean that His apostles will no longer see Him. They only need to share themselves in the fullness of the Kingdom's life on the day of Pentecost. But that still lies ahead of them. For now they sit and look at the sky, until at last God's messengers who appeared from there remind them that their place is not here, but in Jerusalem, where they were commanded to be.