One idea of how the gospels came about is called the two-source theory or the two-source hypothesis. This theory postulates that Mark was written first because both Matthew and Luke contain almost all of Mark while each adding additional information. Matthew contains approximately 92 percent of Mark’s content, while Luke contains approximately 58 percent of Mark. As is observable, both Matthew and Luke also contain much more information not included in Mark. The two-source hypothesis puts forth the idea that both Matthew and Luke used Mark as one source while also using a second, unknown source to compile the rest of the materials in their gospels. This second source is often referred to in scholarly circles as “Q.” Thus, the two-source hypothesis addresses the Synoptic Problem by postulating that Mark was written first, both Matthew and Luke used Mark as a source in writing their gospels, and Matthew and Luke used an additional source we call “Q.”
Luke gives a helpful statement regarding the two-source hypothesis. Note what he states in the prologue to his gospel in Luke 1:1–4: “Many have undertaken to draw up an account of the things that have been fulfilled a among us, just as they were handed down to us by those who from the first were eyewitnesses and servants of the word. With this in mind, since I myself have carefully investigated everything from the beginning, I too decided to write an orderly account for you, most excellent Theophilus, so that you may know the certainty of the things you have been taught.” From this statement, we can learn helpful facts about how these gospels came about. Note that Luke says that “many have undertaken to compile a narrative” (ESV) about Jesus. He also notes that “eyewitnesses and ministers of the word have delivered” (ESV) this information.
Thus, when Luke puts together his “orderly account” of the life of Jesus, he is using multiple sources, including what appears to be written narratives about various events in the life of Christ. Some may have recorded several events of His life or just one or two. If Luke is using the Gospel of Mark as a source, that clearly is a large narrative record. It also seems that Luke is using oral accounts from “eyewitnesses.” In Luke 2:51, we find that Jesus’ mother, Mary, “treasured all these things in her heart.” “These things” are events in the life of the young Jesus. It is likely that Luke spoke with Mary in putting together his gospel.
The “ministers of the word” Luke mentions very well may include some of the original apostles who were used of God to start up the church as recorded in Acts. In regard to eyewitness accounts as well as written narratives of the life of Christ, it is helpful to remember Jesus’ words in John 14:26 where He tells His disciples that the Holy Spirit will “teach you all things and will remind you of everything I have said to you.” This affirms that the gospel writers were compiling and writing down accounts of the life of Jesus from reliable, Holy Spirit-inspired words and recollections of Jesus’ followers.
In conclusion, scholarly topics such as the two-source hypothesis can be helpful in understanding how God, through the Holy Spirit, brought about His gospels. Regardless of whether we ever come to a place of confidence regarding exactly how the gospels were compiled, we are confident that it was ever and only by the power and guidance of God the Holy Spirit.