Now, after having investigated everything carefully from the beginning, I have also decided to write a carefully ordered account for you, most honorable Theophilus. I want you to have confidence in the soundness of the instruction you have received. (Luke 1:3-4, CEB)
Luke wrote so Theophilus could know the truth that he had already been taught. The NASB suggests in a footnote that the reference is to oral instruction. Theophilus has heard the teaching, but a well-ordered account written down will give him confidence in the soundness and exactness of what he has heard, or so Luke hopes.
I find myself wondering what it means to say the gospel exists as a written book to help bolster our confidence in the things we have learned by other means. The gospel comes after, not before, the teaching about the things that have been fulfilled among the believers. It answers the question: Can I trust what I am being told and what I have seen?
This suggests to me a couple things. First, in this account, Luke’s gospel is not in the first instance for shouting to the unbelieving world. It is for ordering and bolstering the things the community already says and does. The gospel, in other words, is the book of the church and for the church. Second, the Bible is a means of grace. It is given by the Holy Spirit to make us “wise unto salvation.” (Those who know the work of William J. Abraham know I am following him on this second point.) The Gospel of Luke exists to lead us into spiritual maturity and to shape our faith in Jesus Christ, but the actual written book itself depends on faith if it is to be read well.
I am not certain that this is what Luke intends, but it does match my own experience. Coming to Christ in the mainline church, I barely read the Bible before my baptism as an adult. In important ways, reading the Bible has helped me understand what I had already come to believe. For me, at least, casual dalliance with the Bible did not lead to faith, but faith — even a faith I could barely explain — led me to the Bible.
Luke wrote his gospel for me, too.