As shocking as they may be, the provocative sermons of Barack Obama's pastor come out of a tradition of using the black church to challenge its members and confront what preachers view as a racist society.

More than three decades ago, the Rev. Jeremiah Wright Jr. took over a small, demoralized congregation on Chicago's impoverished South Side and built it into the largest church in the liberal, mostly white United Church of Christ.

At the 8,000-member Trinity United Church of Christ, the slogan "unashamedly black and unapologetically Christian" has meant preaching about divestment during South Africa's apartheid era. It has also meant fighting poverty, homelessness and AIDS at home.

The pastor's experience is grounded not only in the civil rights movement, but also in 1960s black liberation theology, which applies the Christian Gospel to contemporary struggles against race-based oppression.

"The whole generation that Reverend Wright represents is expressing what they call a righteous anger, the anger from the failed promises of America," said Dwight Hopkins, a professor at the University of Chicago Divinity School. "The prophetic anger is toward expanding the democracy, expanding it so all citizens can walk through the door of opportunity."

Often lost in the attention paid to Wright's fiery sermons is the typical conclusion, Hopkins said -- that despite all obstacles, you are a child of God and "can make a way out of no way."

Though Trinity United Church of Christ is more Afrocentric and slightly more political than most black churches, "even conservative black churches talk about racism in a way that many whites would find wounding or offensive," said Gary Dorrien, a religion professor at Columbia University in New York.

"Most white Americans have a very limited capacity for dealing with black anger or acknowledging their own racial privileges," Dorrien said.

Wright does not focus his ire on white America alone, said Martin Marty, a retired professor of religious history who taught Wright at the University of Chicago.

"He is very hard on his own people," Marty said. "He criticizes them for their lack of fidelity in marriage, for black-on-black crime. He is not saying one part of America is right and one is wrong."

Obama and others also have highlighted Trinity's extensive social safety net. It offers college placement help, drug and alcohol counseling, a credit union, and domestic violence programs.

Wright retired last month.