Citing from the Quran at the close of his letter, he says that if Americans "repent" of their "injustice," they will be blessed with many gifts. "We should all heed the divine Word of the Holy Qur'an," he says.
The context of this particular verse (28:67-28, Sura "Al-Qasas," or The Narration), is very clear. It follows a graphic description of destruction and devastation that will befall those who fail to repent of their injustice.
It also sets out the terms of the tradition Muslim warning to the enemies of Allah. "And never will your Lord destroy the towns until He sends to their mother town a Messenger reciting to them Our Verses." This is is precisely what Ahmadinejad is doing in his letter.
Dump Bush, allow the Muslims to destroy Israel, and adopt Islam — or else you will be destroyed. This is Ahmadinejad's message. Read the whole thing.