The Pope says in his discourse that the irrationality and arbitrary nature of the Islamic god means that said god could do anything, even command idol worship! In other words, the Islamic god is chaos and nihilism, having no reason or structure within himself or his creation and communicating with human beings solely through arbitrary laws and commands.
It was a great address, not exactly a light read, but worth reading from start to finish. I read it in Spanish, but it may be on the Vatican website in English now.
Yup, NYer has a link to the English translation on the Vatican's Web site in reply #1.
Those are two very different things, potentially. Did he say the Muslim concept was that God has no reason within himself? Or only that his reason is inscrutible to man?