It was one of the most powerful talks in relation to the war on terror—which many consider World War IV—given by an international leader and it was delivered by the Holy Father.
This article from the Ethics and Public Policy Center looks at what has happened since.
“In the flood of commentary surrounding the tenth anniversary of 9/11, I found but one reference to a related anniversary of considerable importance: the fifth anniversary of Pope Benedict XVI's Regensburg Lecture. That lecture, given the day after the fifth anniversary of 9/11 at the pope's old university in Germany, identified the two key challenges to 21st century Islam, if that faith of over a billion people is going to live within today's world in something other than a condition of war. On the fifth anniversary of Regensburg, therefore, it's worth reviewing what the Pope proposed, not least because the 9/11 anniversary commentary assiduously avoided the question that the Holy Father courageously confronted: the question of what-must-change in Islam in the future, to prevent an ongoing global war of Islam-against-the-rest.
“Benedict XVI made two proposals at Regensburg.
“Islam, he suggested, must find a way to affirm religious freedom as a fundamental human right that can be known by reason and that includes the right to change one's religion—and it must find this "way" from within its own religious, legal, philosophical, and theological resources. The question is not one of surrender to certain secularist conceptions of public life, any more than it was when Catholicism confronted political modernity and found a solution in the Second Vatican Council's Declaration on Religious Freedom. The solution has to come from within, in what Christian theology would call a "development of doctrine."
“Secondly, Islam must find a way—again, from within its own religious and intellectual resources—to affirm a distinction between religious and political authority in a just state. This need not and indeed cannot mean a radical "wall of separation" between the two, based on some (mis)conceptions of the American constitutional order. It might mean something like what the Catholic Church did during the late 20th century, when Catholic scholars reached back into the fifth century and rediscovered a traditional distinction between priestly and imperial authority: a tradition whose deepest roots go back to the Lord's own distinction between what is owed to Caesar and what is owed to God [Matthew 15.21].
“Despite there being largely ignored during the 9/11 anniversary, these do seem to be the two key issues. An Islam that affirms religious freedom, including conversion from one faith to another, and that buttresses that affirmation through its own religious self-understanding and the arts of reason, is an Islam with which "the rest" can live at ease, and in enriching ways. An Islam in which religious and political authority are distinct, if related, is an Islam in which a genuinely civil society can begin to take root—and a robust civil society is one barrier against the corrupt authoritarianism that has bedeviled Islamic countries for centuries. A robust civil society in which there is room for religious freedom and multiple political perspectives is also essential to realizing the promise of today's "Arab Spring"—which could give birth to a hot summer and a bitter winter if its chief accomplishment is to effect a change from secular political authoritarianism to religiously-warranted political authoritarianism.”