The Babalu Blog (now on the blogroll) has the full text of his resignation in Granma. The key line: "And I reiterated in that letter that …I never forget that ‘all of the world’s glory fits in a kernel of corn. Therefore, it would be a betrayal to my conscience to accept a responsibility requiring more mobility and dedication than I am physically able to offer. This I say devoid of all drama."
Castro's letter confesses to a long health crisis; of which he was unsure he'd emerge alive. He apparently came through better than he hoped. But the sands were running out for him. And although he casts his resignation as the selfless act of a man determined to give way to younger leaders, a close reading of his letter indicates that he still hoped to hang on until it became plain his strength was no longer equal to his desire for power.
Ominously, Castro has no intention of giving up his power entirely. He intends to remain, like some kind of spectral force, the voice behind the curtain.
This is not my farewell to you. My only wish is to fight as a soldier in the battle of ideas. I shall continue to write under the heading of ‘Reflections by comrade Fidel.’ It will be just another weapon you can count on. Perhaps my voice will be heard. I shall be careful.
Several of Babalu's commenters noted that Fidel's resignation now forces a string of long delayed actions. First, Raul Castro (Fidel's brother who is no more than a few years younger and a drunk) must now emerge from the shadow of the old leader; and equally important, US politicians especially in the Democratic party, who must face the fact that the Countdown has begun.