It began as a carefully constructed, formal speech. But in his heart, Martin Luther King wasn't a speech-giver. He was a preacher. So as his message moved along forty years ago today, he began departing from his text. A woman behind him piped up, "Tell 'em about the dream, Martin." Here's how Taylor Branch (Parting the Waters) describes what happened: "The 'Dream' sequence took him from Amos to Isaiah, ending, 'I have a dream that one day, every valley shall be exalted . . .' Then he spoke a few sentences from the prepared conclusion, but within seconds he was off again, reciting the first stanza of 'My Country 'Tis of Thee,' ending, 'from every mountainside, let freedom ring.' After an interlude of merely one sentence -- 'And if America is to be a great nation, this must become true' -- he took it up again: 'So let freedom ring.' . . . As King rolled the freedom bells from New Hampshire to California and back across Mississippi, his solid, square frame shook and his stateliness barely contained the push to an end that was old to King but new to the world: 'And when this happens . . . we will be able to speed up that day when all God's children, black men and white men, Jews and Gentiles, Protestants and Catholics, will be able to join hands and sing in the words of the old Negro spiritual, Free at last! Free at last! Thank God Almighty, we are free at last!" With that King stepped suddenly aside . . . ."