What does Acts 1:2 mean?
Luke is writing to Theophilus, who is possibly a Roman official of some sort, about the beginning of the church. He briefly covered Jesus' ascension in Luke 24:50–52 and will go into more detail in Acts 1:6–11. The commands Jesus gave the disciples include the Great Commission (Matthew 28:16–20) and to stay in Jerusalem and wait for the Holy Spirit (Luke 24:49; Acts 1:4–5). Beyond this, no particular commands are recorded, but He did spend time explaining how the Old Testament Scriptures prophesied His death and resurrection (Luke 24:27, 45), and He reconciled with Peter (John 21:15–19), healing the rift Peter had created with his denial (Mark 14:66–72).We have no record of any commands received by the apostles through the Holy Spirit before the ascension, except that they are to choose a replacement for Judas (Acts 1:12–26). After the resurrection, Jesus did give the disciples the Holy Spirit (John 20:22), but it appears to be in the way of the Old Testament. Old Testament God-followers were sometimes filled with the Holy Spirit, but only for a short time, John the Baptist excepting (Luke 1:15). It isn't until Pentecost that the Holy Spirit starts indwelling all believers (Acts 2:1–4). Jesus had told the disciples this must happen. During the last supper, He said, "I still have many things to say to you, but you cannot bear them now. When the Spirit of truth comes, he will guide you into all the truth…" (John 16:12–13). The disciples couldn't fathom the idea of "the church" until they received the Holy Spirit.
At this time, Jesus has about 120 close followers in Jerusalem (Acts 1:15). The apostles mentioned are the eleven remaining of His primary twelve disciples (Mark 3:13–19). Judas has died, rather dramatically, having first hanged himself (Matthew 27:5) and then fallen and literally spilled his guts (Acts 1:18).
The term "apostle" causes some confusion today. The word comes from the Greek root word Apostolos, which simply means someone who is sent out as a delegate or messenger. The "office" of apostle is given only to the original eleven disciples and Judas' replacement, Matthias (Acts 1:23–26). These special apostles had witnessed Jesus' ministry from His baptism to His resurrection (Acts 1:21–22). More generically, Paul (Acts 9:15), Barnabas (Acts 13:2), Titus (2 Corinthians 8:23), and Epaphroditus (Philippians 2:25) were "sent out" to preach the gospel, but they do not have the particular position of authority of the Twelve.
Although the modern church has traveling evangelists and missionaries, we do not have apostles in the same manner as the early church.