The writer of Luke-Acts is committed to the idea that the Gospel is for all people. Like Paul, he insists that it is first of all for God’s people Israel, and like Paul he insists that God’s plan for the message of Jesus is world-wide.
He embeds this concern from the earliest moments of his story. At Jesus’ dedication in the Temple, Simeon celebrates the baby Jesus, calling him God’s salvation… “a light for the revelation of the nations” (Luke 2:32).
There’s another signal Luke uses as well.
In both Luke and Acts the story transitions into the ministry of the main characters in a pericope that includes a biblical prophet anticipating God’s work on behalf of “all flesh” (πᾶσα σάρξ).
In Luke 3 we meet John the Baptist. Like Mark and Matthew, Luke cites Isa 40 in its identification of John: “A voice crying in the wilderness, prepare the way of the lord.”
Luke, however, continues the citation through the bit about valleys being filled and mountains razed, concluding “and all flesh will see the salvation of God.”
At the beginning of Acts, Peter begins his sermon on Pentecost with a citation of Joel 3: “And it will be in the last days, says God, that I will pour out from my spirit upon all flesh.”
With these two biblical citations, Luke signals that the story of Jesus is not just about Israel, but the nations. It is not just about the sons, but also the daughters. It is not just about the the youthful but also the aged. It is not just about the powerful and free but also about the weak and enslaved.
When Jesus teaches his disciples how to read the Bible in Luke 24, he tells them to look and see there an anticipation of the crucified and risen Christ. And he also tells them to look and see the anticipation that repentance for forgiveness of sins will be proclaimed to all nations (beginning from Jerusalem).
Luke models his interpretive guidance.
At the beginning of each book, we hear from the voice of the biblical prophets. God has a plan. And that plan is for all nations and all peoples within them.
The vision and the spirit are for all flesh.