VERSES 1-2: The former treatise have I made, O Theophilus, of all that Jesus began both to do and teach, 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: The former treatise that he is talking about is the Gospel of Luke. No one knows who Theophilus was, but his name means lover of God. As Luke states, his gospel was what Jesus did and taught until he was taken up.
Notice that Jesus had given "commandments to the apostles whom he had chosen." What commandments had been given to them? Mat 5:38-39; Mat 10:8; Mat 5:46-48; Mar 16:14-19; Joh 13:14; Joh 20:23; Luk 24:47. The bottom line is that all of these commandments had to do with the Kingdom and not the age of Grace.
VERSE 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: Apparently, suring the 40 days between his resurrection and ascension, Jesus spoke to them the things pertaining to the kingdom of God. That means that Jesus had 40 days to explain to the eleven what was going on. Too many in the church today erroneously think they were ignorant of what was going on. Not true.
Promise of the Father
VERSE 4-5: 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. For John truly baptized with water; but ye shall be baptized with the Holy Ghost not many days hence. They were told not to depart from Jerusalem but to wait for the promise of the Father. What was that promise? The promise of the Holy Ghost as foretold in Joel 2:28-32. So they were to wait until the prophecy of Joel to occur.
Note: Red letter editions of the Bible did not come about until 1899. However, it appears that John the Baptist said this and not Christ, e.g., Mat 3:11; Luk 3:16.
VERSE 6: When they therefore were come together, they asked of him, saying, Lord, wilt thou at this time restore again the kingdom to Israel? Notice that the apostles were still looking for an earthly kingdom! Throughout our Lord's ministry, they were constantly concerned about a kingdom. Why? - John the Baptist's first words were "Repent for the kingdom of heaven is at hand" in Mat 3:2. Our Lord's first words were also, "Repent for the kingdom of heaven is at hand" in Mat 4:17. The Beatitudes of Matthew 5 are all about the kingdom! There entire message was the gospel of the kingdom, e.g., Mat 4:23. Anyone who says that we are in the kingdom today needs to actually read the text!
Yes, they fully expected the kingdom to be restored. Not in their hearts either, but a physical kingdom from which they would rule with Christ (Mat 19:28).
VERSE 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. Notice that he did not correct them. Instead, he just said that it was not for them to know. The bottom line is that the kingdom offer was still on the table at this time.
VERSE 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. While he refused to elaborate on the timing of the restoration of the Kingdom, he did tell them that it would be preceded by the outpouring of the Holy Ghost who would come and empower them to take the message to Jerusalem and beyond just like he told them in Mat 24:14. Only the Kingdom is view here and nothing beyond that, i.e., the church.
VERSE 9: And when he had spoken these things, while they beheld, he was taken up; and a cloud received him out of their sight.
Why did Jesus have to ascend? The only passage that speaks about it that I can find in Eph_4:9-10 and it says "that he might fill all things". It speaks of reigning or overseeing.
Also, Psa_110:1 makes it sound like he was expected to do so by the God the Father until "I make your enemies a footstool for your feet."
On another note, when it says "a cloud received him" it may be referring to a heavenly hosts rather than normal atmospheric clouds.
VERSES 10-11: And while they looked stedfastly toward heaven as he went up, behold, two men stood by them in white apparel; 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. The two men wearing white apparel are obviously angelic beings, perhaps part of the cloud in v.9. The Bible also says that he is going to return with clouds (Mat 26:64; Mat 24:30; Rev 1:7). The clouds as present at the rapture of the church (1Th 4:17) and in regards to the two witnesses (Rev 11:12).
Interesting that the angels asked them "why stand ye gazing up into heaven?" The Apostles had a lot of work ahead of them. They had to prepare the nation of Israel for what was to come: the Tribulation, the Second Coming, and the Kingdom. There were going to do this by still proclaiming the Gospel of the Kingdom (Mat 24:1-31). This is not the message or mission of the church. We are not preparing the world for a kingdom or a king necessarily. Our mission is heavenly (Php 3:20). Our message is not about the Kingdom, but about individual salvation. Luk 19:11-28 speaks directly to the ministry of the Apostles.
Notice also that 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. That is the very same Jesus, the same way you saw him go, he will return in like manner. Just as he physically left he will physically return. Just as he left from the Mount of Olives, he will return to the Mount of Olives (Zec 14:4; Zec 14:9). This is not referring to the Rapture, but the Second Coming. The Rapture is for the church while the Second Coming is for the nation of Israel.
A Replacement for Judas
VERSE 12: Then returned they unto Jerusalem from the mount called Olivet, which is from Jerusalem a sabbath day's journey. A sabbath day's journey is slightly over a mile. Notice that they were still concerned with the law.
VERSES 13-15: And when they were come in, they went up into an upper room, where abode both Peter, and James, and John, and Andrew, Philip, and Thomas, Bartholomew, and Matthew, James the son of Alphaeus, and Simon Zelotes, and Judas the brother of James. These all continued with one accord in prayer and supplication, with the women, and Mary the mother of Jesus, and with his brethren. And in those days Peter stood up in the midst of the disciples, and said, (the number of names together were about an hundred and twenty,) Luke now names the apostles present by name. Of course, Judas is gone. Altogether, there was about 120 present. Notice also that it says that they were all in one accord in prayer and supplication. That is important to know since some today say that Peter messed up in what they are about to do.