Acts Chapter 1

Who is "Theophilus" (Acts 1:1)?
See Theophilus.

Who is "I" (Acts 1:1)?
Luke, who accompanied Paul on his missionary journeys and recorded what Paul recounted and taught.

What is the "former account" (Acts 1:1)?
The Gospel of Luke (see Theophilus and Luke).

With which event does the Gospel of Luke close?
Jesus' ascension to heaven.

Then why did Luke write that the Gospel of Luke records what Jesus "began" (Acts 1:1) to do and teach?
What Jesus began to do and teach during His earthly ministry, His Holy Spirit - the "Helper" or the "Spirit of truth" - continued to do and teach after His ascension, just as Jesus had told His disciples in advance: “But now I go away to Him who sent Me, and none of you asks Me, ‘Where are You going?’ But because I have said these things to you, sorrow has filled your heart. Nevertheless I tell you the truth. It is to your advantage that I go away; for if I do not go away, the Helper will not come to you; but if I depart, I will send Him to you. And when He has come, He will convict the world of sin, and of righteousness, and of judgment: of sin, because they do not believe in Me; of righteousness, because I go to My Father and you see Me no more; of judgment, because the ruler of this world is judged. I still have many things to say to you, but you cannot bear them now. However, when He, the Spirit of truth, has come, He will guide you into all truth; for He will not speak on His own authority, but whatever He hears He will speak; and He will tell you things to come. He will glorify Me, for He will take of what is Mine and declare it to you. All things that the Father has are Mine. Therefore I said that He will take of Mine and declare it to you.” (John 16:5-15)

What qualified Luke to record what Paul recounted and taught?
Luke was a doctor - "Luke the beloved physician and Demas greet you." (Colossians 4:14) - and doctors were trained to record things accurately.

Did Luke record only what he was told?
After he began to accompany Paul, he also recorded what he witnessed.

Where did Luke begin to accompany Paul?
Please pay close attention to the pronouns as you read the following passage from Acts 16:7-10. The first "they" refers to Paul, Silas and Timothy: " 7 After they had come to Mysia, they tried to go into Bithynia, but the Spirit did not permit them. 8 So passing by Mysia, they came down to Troas. 9 And a vision appeared to Paul in the night. A man of Macedonia stood and pleaded with him, saying, “Come over to Macedonia and help us.” 10 Now after he had seen the vision, immediately we sought to go to Macedonia, concluding that the Lord had called us to preach the Gospel to them." Did you catch the shift from "they" to "we" in Acts 16:10 when Luke joined Paul, Silas and Timothy in Troas?

Where is Troas?
Troas is a port city near the northwestern corner of what is Turkey today. The city's ancient name is Troy (see Phrygia, Bithynia, Mysia).

To where did Luke accompany Paul?
Rome, where Paul wrote to Timothy: "Be diligent to come to me quickly; for Demas has forsaken me, having loved this present world, and has departed for Thessalonica - Crescens for Galatia, Titus for Dalmatia. Only Luke is with me..." (2 Timothy 4:9-11)