Why does King use this allusion? to share historical precedent to emphasize the morality of his cause to define the purpose of his travel to compare the goals of famous leaders

The question is missing the following excerpt from Dr. Martin Luther King's "Letter from Birmingham Jail:"

Just as the Apostle Paul left his village of Tarsus and carried the gospel of Jesus Christ to the far corners of the Greco Roman world, so am I compelled to carry the gospel of freedom beyond my own home town.

Answer:

To emphasize the morality of his cause

Explanation:

King wrote this letter while he was in prison for being a participant in a nonviolent demonstration against segregation. The letter was a response to the open letter "A Call for Unity" by eight white Alabama clergymen where they criticized demonstrations as a means to end segregation, told black people to be patient, and called King "an extremist."

So, in the excerpt provided, King uses the allusion to the Apostle Paul to link the civil rights campaign's cause to the Christian traditions and emphasize the righteousness or morality of his cause and actions.