Contrary to what people might think, Islam as much divides Iran and the rest of the Arab world as it unites them. Shia Islam can be described as an Iranian nationalist adaptation of Islam. There are a number of fundamental differences which not only divide Shiite and Sunni Islam but also make them direct contraries.

The most obvious and telling difference is that Shiite Islam is Messianic whereas Sunni Islam is not. Messianism is at the heart of Zaroastrianism too - the first theistic religion from which Judaism and thus Christianity sprang. That makes Shiite Islam perhaps closer in its philosophy to the aforementioned "Western" religions than to Sunni Islam.

Equally important is progressiveness. It might seem odd to describe Shiite Islam as progressive but in theory it is. The word Sunni actually comes from the word "sonat" which means tradition. Sunni Islam is conservative, it believes in the maintenance of traditions. But at the heart of Shiite Islam is the concept of just rebellion. All the Shiite Imams (except Imam Mahdi who is hidden and is to return) were murdered because of their opposition to the political powers of the day. Thus Shiism is at heart stridently ant-injustice and therefore progressive. Of course, the current regime are far from adequately representing this aspect of the religion that they profess to practice.