Verse 1 establishes the fact that Luke (a Gentile) is the writer, "the former treatise" being his Gospel (Luke 1:1-3). In that case Theophilus is addressed as "most excellent," manifestly a public official of importance. It may be likely that he gave up such an office when brought to God by the gospel, for he is not so addressed in Acts. Luke wrote of "all that Jesus began both to do and to teach." Acts therefore is a continuance of this same work of the Lord Jesus, though He Himself has been taken up into heaven. He had first given commandments to the apostles "by the Holy Spirit." Since He spoke by the Spirit then, He is no less capable of speaking by the Spirit now, though He is physically absent.
During a period of forty days after His death and resurrection He presented Himself as living to His disciples, the fact of His resurrection being attested by "many infallible proofs." Every reader may find these easily for himself if he cares to enquire into Scripture. This is absolutely basic to Christianity, being insisted upon continually through the book of Acts. Without it the apostles would have been as weak as water and their message futile: with it came a power and conviction that wrought marvellous and precious results. Those things of which He spoke "pertaining to the kingdom of God" were not, we may be sure, referring to its future state of glory and majesty, but rather to its present form as being identified with a rejected Messiah, as the following verses indicate clearly.
Notice, as to the introduction of the church dispensation, assembling together is a prominent feature of it (v.4-6), as will be seen throughout Acts. The Lord tells them to wait for the promise of the Father, as seen also inLuke 24:49. He speaks of this as their being baptized with the Holy Spirit, an expression used seven times in scripture. Only 1 Corinthians 12:13 explains it as being the uniting together in one body all believers, Jewish or Gentile, bond or free. It is a great blessing therefore that belongs to all believers unitedly, not simply a personal blessing, but true of the whole church of God since the Spirit has come.
Together they ask Him if this will mean the restoration of the kingdom to Israel. But He tells them it is not for them to know the times or seasons: this matter was in the Father's own authority. He did not yet tell them that a totally new dispensation was being introduced, but wisely leads them a step at a time. They would learn that times and seasons had nothing to do with the assembly, in contrast to Israel, and that Israel was to be set aside while the assembly was being called out from among all nations.
But they would receive power ("dunamis"), not authority, as the word "power" means in v.7, but vital energy, through the coming of the Holy Spirit upon them. This would enable them as witnesses to Him, beginning at Jerusalem, but spreading out to Judea and Samaria, then the far reaches of the earth, -- a wonderful contrast indeed to a kingdom confined to Israel.
Verse 9 of course overlaps the end of Luke's Gospel, the ascension being spoken of there also. The disciples witnessed this, and a cloud receiving Him out of their sight, the cloud indicating some measure of obscurity, for there are things concerning His bodily ascension to heaven that are beyond our present limit of understanding. Only in Acts do we read of the angelic appearance of the two men at this time. We can understand the disciples gazing up into heaven, but they would see Him no longer in this way. He will yet come in like manner to the same location, the mount of Olives, when He takes His rightful place of glory and majesty. There is no suggestion as to how long the time would be, and of course the rapture will take place before this. Meanwhile, the day of grace has lengthened out far beyond what we might have imagined.
Returning to Jerusalem, they gather in a room on an upper level, which was manifestly of a large size for 120 to be present at once, and for eleven to live there during their visit in Jerusalem. Prayer and supplication were paramount for the time. Mary the mother of Jesus is mentioned here for the last time in scripture, her name held in honor, but no undue place of prominence given her. It is precious to see "His brethren" mentioned. Before His death they had not believed in Him (John 7:5): evidently His death itself had broken down their stubborn wills.
Peter's addressing the company was based upon Old Testament scriptures, therefore his proposal is evidently correct, for the Spirit of God had not yet come. The scripture must be fulfilled, as he says, concerning Judas, who had been numbered with the apostles, but fell into iniquity, the reward of which purchased a field. Matthew tells us he hanged himself (Ch.27:5): it appears that the rope broke so that he plunged headlong, causing all his bowels to gush out. This was so well known in Jerusalem that the field purchased with the betrayal money was called "the field of blood."
Peter quotesPsalms 41:9 to the effect that another should take the office of Judas. On this scriptural basis they act, being careful that the man appointed must be one who had companied with them during all the time of the Lord's ministry on earth until His ascension, for he must be a competent witness to the resurrection of Christ. Evidently they chose the two men most qualified for this, then prayed concerning them that the Lord would indicate by lot His choice in the matter. Again, they no doubt depended on the instruction of Proverbs 16:33: "the lot is cast into the lap; but the whole disposing thereof is of the Lord." After the Spirit of God had come, this would be no longer the way of God's making His mind known. Some have objected that Peter and the apostles were not guided by God in this matter, but scripture makes no comment one way or the other, and it is wiser that we leave the matter as scripture does.