Gardena, California (CNN) -- About 300 mourners remembered legendary singer Etta James on Saturday as an authentic voice whose velvety vocals bridged genres from blues to rock.
Another legendary singer, Stevie Wonder, gave a musical tribute to James at her funeral: He played the electronic keyboard and sang his "Shelter in the Rain." He then performed on the harmonica and sang The Lord's Prayer.
Also performing at the service was Christina Aguilera, who sang James' signature song "At Last" and ended her rendition to a standing audience with a farewell directed at James' casket: "May you rest in peace."
After the service, Aguilera told CNN that James was her idol.
"It was so emotional," Aguilera said. "I went through the lyrics last night, and I did rehearsal ... and it took on a whole new meaning having been invited by her close friends and family to sing that classic song at her service. And I started crying every time I started to sing it, and I thought, 'My gosh, what if that happens tomorrow? I just want to do justice to Etta James. She meant the whole world to me, and it was a huge honor to be here today."
The Rev. Al Sharpton presided over the funeral in southern California where James was raised, and he began the service by reading aloud a note from President Barack Obama, who said that James' talents transcended genres.
Obama wrote that James will be remembered for her voice, Sharpton told family and friends at Greater Bethany Community Church City of Refuge in Gardena.
"I know she will be sorely missed by all those who knew and loved her," the president's note said, according to Sharpton.
James died January 20 at the age of 73 of complications due to leukemia at a hospital in Riverside, California. She would have turned 74 last Wednesday.
Her assertive, earthy voice lit up such hits as "The Wallflower," "Something's Got a Hold on Me" and the wedding favorite "At Last."
Sharpton said that James first developed her voice in a local Baptist church as a little girl singing gospel -- which "was just race music when she started." When she died this month, he said, her photograph appeared on the front page of the New York Times, a mark of a triumphant life.
"Etta James has given us too much to work with," Sharpton said. "Etta James was for real. She was authentic.
"I think it was her authenticity that was part of the charisma that drew people to her," Sharpton said. "She really became a bridge of American culture that changed the culture of the world. It was Etta James that bridged rhythm and blues with rock and roll.
"Etta James helped break down the culture curtain of America before the Civil Rights Act of 1964," Sharpton eulogized. "She was able to get us to sing the same rhythms and melodies."
Evoking the title of a signature song of James, Sharpton raised his voice: "At last, you can find peace now!
"At last, you can get the gratitude of the savior now," Sharpton continued. "Etta, you made it, you're going home. At last! At last! At last!"
Donto James, the older of James' sons, recalled how his mother had a soft spot for anyone who lost their mother. Donto James played drums in his mother's band.
"She'd give them a job like that," he told the mourners.
"She loved her band. She would pick up anybody to work for," he added.
In a lighter moment, the son recalled how high-spirited his mother was.
"She was feisty, very feisty," he said. "I found myself as a son trying to clean up some things. I should have tried to stay out of it. I don't know what I was doing."
Fans got the opportunity Friday to bid farewell to James during a public viewing at the Inglewood Cemetery Mortuary. Hundreds of people waited for hours to sign registers and attend the viewing for James.
The family has requested donations be sent to The Rhythm & Blues Foundation.
The powerhouse singer, known as "Miss Peaches," first hit the charts as a teenager, taking "The Wallflower (Roll With Me, Henry)" -- an "answer record" to Hank Ballard's "Work With Me, Annie" -- to No. 1 on the R&B charts in 1955.
She joined Chess Records in 1960 and had a string of R&B and pop hits, many with lush string arrangements.
After a mid-decade fade, she re-emerged in 1967 with a more hard-edged, soulful sound.
Throughout her career, James overcame a heroin addiction, opened for the Rolling Stones, won six Grammys and was voted into the Rock and Roll Hall of Fame.
Despite her ups and downs -- including a number of health problems -- she maintained an optimistic attitude.
"Most of the songs I sing, they have that blue feeling to it. They have that sorry feeling. And I don't know what I'm sorry about," she told CNN's Denise Quan in 2002. "I don't!"
Through it all, she was a spitfire beloved by contemporaries and young up-and-comers.
"Etta James is unmanageable, and I'm the closest thing she's ever had to a manager," Lupe De Leon, her manager of 30-plus years, told CNN.
British songstress Adele named James as one of her favorite singers, along with Aretha Franklin.
"If you were to look up the word 'singer' in the dictionary, you'd see their names," Adele said in an interview.
Etta James was born Jamesetta Hawkins in south Los Angeles to a teen mother and unknown father. She suspected her father was Rudolph Wanderone Jr., the famous pool hustler known as Minnesota Fats.
CNN's Denise Quan in Gardena, Alan Duke and Todd Leopold contributed to this report.