In this letter, Martin Luther King Jr. largely makes allusions to the Bible, reflecting his religious position as a reverend. However, these allusions also show how committed he was to racial justice: he took on such problems with a spiritual fervor. He tries to connect with his audience on a religious level by appealing to those beliefs.

Early in the letter, King compares himself to the Hebrew prophets of the Old Testament and to Paul of Tarsus in the New Testament:

But more basically, I am in Birmingham because injustice is here. Just as the prophets of the eighth century BC left their villages and carried their "thus saith the Lord" far beyond the boundaries of their home towns, and 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. Like Paul, I must constantly respond to the Macedonian call for aid.

King makes these comparisons to argue against those who have criticized his work in Birmingham as "unwise and untimely." He approaches his mission with an urgency that is comparable to these biblical figures. Just as they felt compelled by God to seek justice, so too does King. This comparison is also meant to make the reader think that in their own time, these biblical messengers were also seen as just making trouble despite the importance of their work.

When responding to the argument that his civil disobedience is troubling, King makes an allusion to the Book of Daniel, in which the devout Jews Shadrach, Meshach, and Abednego disobey the laws of the Babylonian king to stay true to "a higher moral law." King makes the same point about the early Christians, who refused to compromise their faith by paying homage to Caesar as a divine being. On a more secular note, he alludes to the Boston Tea Party, a defining moment in American independence, as civil disobedience. He is essentially giving his actions and beliefs proper precedents in terms at once religious, moral, and political, defending himself from his critics.