Mark Durie writing at First Things, On The Square:
Comprising 57 states, the Organization of the Islamic Conference is the second-largest intergovernmental institution in the world after the UN. It is a unique body. A political organization, it pursues a religious mission. The charter of the OIC makes clear that it exists, not only to promote the economic and humanitarian goals of member states, but also to ‘defend’ and ‘disseminate’ Islam itself. The OIC even has a ‘Department of Islamic Propagation (Dawa) Affairs’ dedicated to establishing Islam.
It would be inconceivable for nations with Christian majorities to band together to form an intergovernmental organization devoted to advancing Christianity and the global interests of the Christian Church. The existence of the OIC is testimony to the reality that mainstream Islam recognizes no distinction between politics and religion.
David Goldman, writing in the comments:
The whole concept of an ambassadorship to the OIC is questionable from the outset: what if Christian countries were to form an “Organization of Christian States?” The idea is self-contradictory, for there are no Christian states, only states with a majority Christian population, in which religion has no voice in governance. But there are very few secular Muslim-majority countries, and the most important of those, Turkey, is gradually reverting to an Islamic state. In other words, the OIC only could exist to begin with because Islam is hard to imagine without theocracy (I did not say impossible, but there is no persuasive counter-example). And the OIC only exists to discuss general principles among commonly-minded states. The general principles that it exists to discuss are antithetical to the American (or UN Charter) concept of human rights, precisely because they are premised upon theocracy, and are hostile to freedom of religion.