Question

I have the honor of serving as president of the Southern Christian Leadership Conference, an organization operating in every southern state, with headquarters in Atlanta, Georgia.

What is King’s purpose for including this sentence?
to emphasize his own Southern roots
to illustrate the depth of his religious faith
to establish his professional credentials
to explain his ties to the city of Atlanta

Answer 1

to establish his professional credentials

He cites his role and the organization's reach to show his authority and legitimacy as a civil-rights leader (and to counter the charge that he's an outsider).