The sources of Luke’s gospel are the records given him by many eyewitnesses (Luke 1:2). That is, he was not the eyewitness, but his record is an account of the eyewitness testimony of others. This included the testimony of the Twelve (verse-2), which was believed by so many throughout the world (verse-1), of which Theophilus is an example (verse-3).
It may be Luke drew from a common record compiled by the apostles (verse-2). This record could have been the basis of both Matthew and Luke, which is the reason why so many verses have a word for word agreement. Nevertheless, Matthew does not follow Luke nor does Luke follow Matthew. They were written for different reasons at different times by different men. Luke is a chronological record, but Matthew is not. Matthew was more interested in collecting similar teachings of Jesus and grouping them together for the purpose of teaching new believers. Rabbis used similar repetitive measures to help their disciples commit their teachings to memory. Furthermore, Matthew was written to convince Jews of the truth, while Luke was written for Gentiles, like Theophilus.
Luke diligently traced out his information to its source (verse-3). In other words, he is saying that he personally interviewed eyewitnesses and recorded their testimony. This means that Luke’s account was not compiled from only the record of the Twelve. For example, more than any other Gospel account, Luke records what Mary thought and said. Could this have been done without Mary, the mother of Jesus offering her testimony? Luke compiled a great deal of eyewitness testimony not only for this present thesis, but also for his second thesis to Theophilus (Acts 1:1). Probably Luke journeyed to Palestine and spoke with many of the apostles, James, Mary (the mother of the Lord) and perhaps others like Mary Magdalene, Lazarus and Martha etc. Certainly Acts 1:1 testifies that the author of both accounts is the same person. Acts 16:10 shows that the author of both accounts was a companion of Paul, and the “we” in the text shows that he had just joined Paul in Troas, which is what a man named Luke had done. My point in saying this here is to show an internal date for both the documents of Luke and that of Acts.
Acts 1:1 argues that Luke had to have been written before the chronicle of Acts was completed, for they were written by the same author for the same person. The book of Acts ends before the death of Paul. Most scholars agree that the deaths of both Peter and Paul took place in 66 CE at Rome. This means that the internal testimony of Luke and Acts, taken together, argue for a date before 66 CE. Luke would have had to be written sometime between 55 and 65 CE, according to its internal argument.
Verse-3 argues that Luke is writing a chronological record. The word he used was kathexes (G2517), meaning “in order, according to the order or succession, successively, consecutively in connected order [The Complete Word Study Dictionary: New Testament; Dr Spiros Zodiates]. In other words, Luke was not merely “harmonizing” the accounts of the Apostles like some men try to do with the Gospels and other books of the Bible. Luke spoke with the eyewitnesses, which would have included some apostles, and was able to determine the order in which things occurred in the life and times of Jesus. Luke, then, wasn’t giving his opinion as to how things fell into place, but he claimed he “carefully investigated” (NIV) everything to its “source” or eyewitness. This, of course, does not imply that Luke recorded “everything” there was to record about Jesus. John says that would be impractical, if not impossible (John 21:25), but “everything” Luke recorded was based upon eyewitness testimony. All this was done so that Theophilus and, presumably, others could know the “certainty of the things” we have been taught (verse-4).
The name “Theophilus” means lover of God. I have heard people say that this could mean Luke wrote to believers in general, because we all love God. This is a possibility, but, personally, I do not believe this proposition is correct. I say this, because Luke addresses him as “most excellent.” This was the manner in which the governors, Felix and Festus, were addressed (Acts 23:26; 24:3; 26:25). I suspect Theophilus was a Roman of some rank, perhaps a magistrate or a centurion who, like Philemon, was the host of a local church (cp. Philemon 1:2).
If the Gospel of Luke was never written, the eyewitness testimony of many who were not numbered with the Twelve would have been lost to us today. As is implied in these first few verses, Luke’s record includes some testimony not in the apostolic records from which much of Luke and Matthew are drawn. It would seem that this is the way of the Spirit of the Lord works within his Church. Success is not an individual matter within the Body of Christ. Rather, we build upon the contributions of other brethren. A man’s name may identify a work in the Lord (viz. The Gospel According to Luke), but often it is not his work alone. For example, I usually study my Bible alone. Yet, even in something as personal as this holy labor, the literary works of many men are before me in the form of commentaries, Bible dictionaries, Biblical history etc. (modern messengers), and they contribute unawares to my fellowship with and my understanding of my Savior and Lord, Jesus Christ.