Oprah Winfrey is returning to scripted television after two decades to star in a show about a black megachurch in Memphis.

Although the television will look a the church in all its flaws, Winfrey told People: "I am not going to do anything that is derogatory toward the church because I am of the church."

Winfrey, 62, plays a manipulative blues club owner in the 13-episode series Greenleaf for her OWN cable television channel that she called "a dream come true."

"What this has taught me is that as big as I have dreamed and as big as the dream that God has held for me, things get even bigger and better," Winfrey said at a screening on Wednesday at the Tribeca film festival, ahead of the show's TV debut on June 21.

Winfrey, also an executive producer, said she saw Greenleaf as continuing the mission behind her long-running chat show that ended in 2011, and her magazine O.

"My real role on earth is to lift the consciousness... It's about showing people new ways of seeing themselves and seeing the problems and flaws and dysfunctions that we all have and being able to lift that just enough that you can see yourself in that," she told the Tribeca audience.

Winfrey, who was nominated for an Oscar in 1986 for her role in The Color Purple, and appeared in movies The Butler and Selma, last had a regular acting TV part in Brewster Place in 1990.

Greenleaf, created by Six Feet Under writer Craig Wright, tells the story of a wealthy African-American family behind a mega-church, their rivalries, secrets and hypocrisies.

Wright said the show takes religion, and its role in the black community, seriously, but also raises questions.

"It is not a soap. It is not a sermon," he said.

"It is a story about a lost faith and an attempt to get it back by setting things right and all the challenges that come your way when you try to fix the system." 

"Do you not think people in the church are flawed?" Winfrey asked reporters from People at the event. "That's why they're going."

Merle Dandridge stars as Grace Greenleaf, the prodigal daughter who returns home after a 20-year rift, and Lynn Whitfield plays family matriarch Lady Mae Greenleaf.

Whitfield said the series represented a departure from other TV depictions of the black community.

"This is a story we have not seen on TV for a long time ... It is not about racial problems or financial difficulty. These people have to deal with themselves and their lives," she said.