The Gospel itself is anonymous
Luke's Gospel never says, “I, Luke, wrote this.” Its opening does tell us a great deal about the writer's purpose. He knew that others had already recorded accounts of Jesus, and he says he carefully investigated the events passed on by eyewitnesses. He wrote an orderly account for a man called Theophilus, so that he could be confident about what he had been taught (Luke 1:1-4).
That honesty matters. We should not pretend the book identifies its author when it does not. Yet the introduction shows a thoughtful writer who cared about accurate testimony, not someone simply passing on a rumour.
It seemed good to me also, having had perfect understanding of all things from the very first, to write unto thee in order, most excellent Theophilus, That thou mightest know the certainty of those things, wherein thou hast been instructed.
Why is it called Luke?
From the earliest centuries of the church, Christians have commonly called this Gospel Luke because they understood Luke, Paul's companion, to be its author. The Bible does not directly connect Luke's name to the Gospel, so this is a traditional identification rather than a line the book states about itself.
The New Testament does introduce a man named Luke. Paul calls him the beloved physician in his letter to the Colossians (Colossians 4:14). In Philemon, Paul includes Luke among his fellow labourers (Philemon 1:24). Near the end of Paul's life, he writes that Luke alone remained with him (2 Timothy 4:11). These brief glimpses fit the picture of a faithful co-worker who travelled and served alongside Paul.
Luke and Acts belong together
The strongest clue within Scripture is the close link between Luke and Acts. Luke begins by addressing Theophilus and explaining why the account was written (Luke 1:1-4). Acts opens by referring to an earlier account, also addressed to Theophilus, about what Jesus began to do and teach (Acts 1:1-2). The natural reading is that one author wrote both volumes.
Together, the books tell one unfolding story. The Gospel follows Jesus' birth, ministry, death, resurrection, and ascension. Acts then follows the risen Jesus' witnesses as the good news moves from Jerusalem outward through the Roman world (Acts 1:8).
The former treatise have I made, O Theophilus, of all that Jesus began both to do and teach, Until the day in which he was taken up, after that he through the Holy Ghost had given commandments unto the apostles whom he had chosen:
What the author wanted you to see
Whether you are reading Luke for the first time or returning to it after years, the central question is not only who held the pen. It is who Jesus is. Luke records Jesus describing his mission as seeking and saving those who are lost (Luke 19:10). He pays special attention to people others overlooked, including the poor, the sick, women, outsiders, and sinners who turned to God.
Luke also makes clear that Jesus' message reaches beyond one nation. At the start of the Gospel, Simeon recognises that God's salvation is prepared before all peoples (Luke 2:30-32). Reading Luke slowly can help you meet Jesus in the story itself, and see why this carefully prepared account has strengthened Christians for centuries.