Barack Obama believes in his voice and his life story. Autobiographical speeches powered his campaign, and he saved his wobbly presidential bid in 2008 with a pensive—and personal—sermon in Philadelphia on the history of race, weaving his own multihued DNA into the tapestry of America. As sweeping as it sounded, that speech also had a narrower political purpose: to put distance between him and the racist rants of the Rev. Jeremiah Wright, in whose Chicago congregation Obama sat for years without uttering a complaint. Obama was so deft, so embracing of our sad history, pain and differences—and so convincing because of his life testimony. It seemed almost incidental that his real aim was to jettison a political liability.

Now comes the ultimate test of autobiographical speechmaking. Obama this week speaks at Cairo University, in the hub of Muslim-Arab culture. Perhaps the results will be Philly II: a skillful blend of grandeur and grit. On one level, he isn't risking much. After all, George W. Bush set the bar so low. All Obama has to do to be a success is elicit applause—rather than a fusillade of hurled shoes.

But he has privately told friends that his goal is far higher: nothing less than to help "reconcile Islam and modernity." He will pay homage to the Golden Age of that culture—its glorious achievements in mathematics, science, literature and diplomacy—and note that Muslim scholars rescued from oblivion the Greek and Roman (i.e., the "Western") canon. He also will draw on the by-now-familiar story of his own life. A Christian son of an African-Muslim father, he spent years in Muslim-majority Indonesia, attending a public school run by, but not suffused with, the teachings of Islam. All of this, Obama thinks, not only allows him, but obliges him, to play a grand role as bridge builder.

I admire his ambition, but want to remind him: Cairo is not Philly, and the Muslim world is not America. During the 2008 campaign, he was on home turf, and the country was ready for his message. Now he's in the crowded bazaar. He is headed to a place where talk isn't cheap, it is dangerous; where soothing words, especially from non-Muslims, are regarded warily at best; and where expectations, if raised too high, can come crashing down with devastating results.

In a sense, Obama has been waiting to give this speech for years. The real planning began months ago. At first, his staff focused on where he would give it. A strong case was made for Indonesia—a home of sorts, but also the most populous Muslim country and one of the most secular. But Obama insiders settled on Egypt. Why? To show that the U.S. does not shy away from philosophical (as opposed to purely military) confrontation with fundamentalists and Al Qaeda—and to back an ally that recognizes Israel, and that, therefore, can help revive the broken peace process in the Palestinian territories.

In the diplomatic community, there is little doubt the president is doing the right thing in Cairo. "President Bush liked to talk about our shared values, but it came off as didactic," said Tamara Wittes of the Brookings Institution. "His escalating series of military interventions left people in Muslim-majority countries feeling imposed upon. Obama's speech is a game-changer, because he's going to say that we are partners and equals."