Overview
Theophilus appears as the addressee in Luke's prologue and at the opening of Acts. Luke writes to him with the stated purpose of providing an orderly, eyewitness account so that Theophilus might know the certainty of the things he had been taught about Jesus Christ and the apostolic witness.
Key Scriptures
"Inasmuch as many have undertaken to compile a narrative of the things that have been accomplished among us, just as those who from the beginning were eyewitnesses and ministers of the word have delivered them to us, it seemed good to me also, having followed all things closely for some time past, to write an orderly account for you, most excellent Theophilus" (Luke 1:1–3, ESV).
"In the first book, O Theophilus, I have dealt with all that Jesus began to do and teach" (Acts 1:1, ESV).
Application
Like Theophilus, seek reliable, eyewitness testimony about Christ through Scripture to deepen your certainty in the gospel.