King was educated as a theologian, with a heavy dose of philosophy, and his Letter from Birmingham Jail is a beautiful discussion of the legitimacy and necessity of civil disobedience, just and unjust laws, and race consciousness:
I suppose I should have realized that few members of the oppressor race can understand the deep groans and passionate yearnings of the oppressed race, and still fewer have the vision to see that injustice must be rooted out by strong, persistent and determined action.
Christians will also be interested in King's criticisms of the conventional American church; for more on that, read today's piece on King in The Chron.
The link above has links, in turn, to the Letter, and a brief historical discussion putting the Letter in context. It's not too long; I highly recommend taking a few minutes to read it.