QUESTION: Why do you think King begins the paragraph with a question? CONCLUDE: How does the rest of the paragraph help answer the question?

I think the implication is rhetorical in nature,

While confined here in the Birmingham city jail, I came across your recent statement calling my present activities “unwise and untimely.” Seldom do I pause to answer criticism of my work and ideas.

King knows why he paused because he is trying to articulate that white clergy has done little to help the Black Civil Rights movement.