At age 14, Aretha Louise Franklin was already a veteran of the black gospel circuit of the 1950s, a segregated world of charismatic preachers and unbridled vocalists who traveled from church to church, bringing a message of joy, belief and salvation. Because her father, Rev. C.L. Franklin of Detroit’s New Bethel Baptist Church, was a spellbinding powerhouse speaker, Aretha was also “Negro” royalty, a child surrounded by the giants of gospel music -- Mahalia Jackson, James Cleveland, Albertina Walker and the young Sam Cooke, who was lead singer of The Soul Stirrers and a teen idol.

For all the gifted people Aretha encountered, this budding singer-pianist was not simply a protégée, but a prodigy. Her gift is apparent in a recording made one Sunday morning at a church service in 1956. Accompanied by piano, a teenage Aretha sings Thomas Dorsey’s classic “Take My Hand, Precious Lord” with extraordinary pitch and control. About four minutes in, the song falls away, and for the next two minutes, the young woman improvises moans, groans and whoops that would, one day, become staples of American singing.

The vocal techniques Aretha was exploring in church had largely been confined, due to racism and tradition, to “Negroes.” But the sound was a product of this country, one that spoke to both Southern roots and gritty big-city reality. It was an improvisational style that demanded the intensity of John Coltrane and the nuance of Miles Davis. It wedded jazz and blues with rhythm and religion. It would redefine vocal artistry in America. It was called soul -- but really, it was Aretha Franklin.

Since the days of slavery right into the ’50s, there had been a kind of musical dividing line between the spiritual and secular worlds. Church singers, steeped in the call-and-response among choir, congregation and ministers, were discouraged by custom and religion from bringing the black churches’ devotional techniques to popular music. The adventurous Ray Charles, who wasn't deeply tied to Christianity, had helped merge the sounds, while Cooke had been one of gospel’s first major stars to abandon devotional music to sing of romantic love.

But, with due respect to both of those men, no one epitomized the musical marriage of the sacred and the profane like Aretha Franklin. She was a child of the church, but Re-Re could get as gutbucket as a bluesman and as sensual as a bordello bedroom. She respected melody but was never confined by written notes, adding complex meanings to songs written by others, whether the composer was Otis Redding (“Respect”), Paul Simon (“Bridge Over Troubled Water”) or The Beatles (“Eleanor Rigby”). Her ability to communicate romantic yearning, thwarted desire and pure pleasure is unmatched in post-World War II American music.

The soul synthesis that so beautifully framed her voice wasn't achieved without trial and error. Her first run of secular recordings, largely made at Columbia Records, now sound like struggling attempts to harness volcanic energy. Jazz standards, Broadway show tunes and pop are heard throughout these recordings, many of which have merit, but failed to fully work artistically or commercially. But while Aretha struggled to find the right setting for her voice, the musical landscape changed around her. By the mid-’60s, a generation of songwriters and singers including Curtis Mayfield, Wilson Pickett, Gladys Knight and David Ruffin had erased the separation between R&B and gospel, reshaping the sound of black pop music and in so doing affecting the sound of all music in that vibrant era of exploration. The soul sound -- with its attitude reflecting the progressive ideas of the civil rights movement -- was as dominant for a young person then as, say, trap is today.

In 1967, Aretha signed with Atlantic Records, where she was mentored by A&R man Jerry Wexler and recorded the brilliant “I Never Loved a Man (The Way I Love You),” featuring the legendary all-white Muscle Shoals, Ala., rhythm section augmented by New York-based saxophonist-bandleader King Curtis (who co-wrote two songs on the album). The LP is the big bang that heralded her ascendancy to the “Queen of Soul” throne. A crucial element on it, as well as on subsequent classic recordings, was that Aretha was not just a singer, but a glorious piano player with a tremendous sense of rhythm and understanding of how to support her own voice. Listen to the ringing chords she plays on “Don’t Play That Song (You Lied)”; it makes you wish she had cut an album of her just riffing on 88 keys.

Though she made scores of classic recordings and live appearances, the one essential album you must hear in order to understand Aretha Franklin is Amazing Grace, recorded live over two nights at Rev. James Cleveland’s Los Angeles church in 1972. Backed by a huge choir and an expert R&B rhythm section with Aretha on piano, she matches the gospel power she had processed as a teen with the wisdom and toughness of an adult life. Performances on the record are so powerful they’ll make you cry.

Director Sydney Pollack filmed both nights of the Amazing Grace performances, but the footage lay forgotten in the Warner Bros. vaults for decades. A movie has been made of the shows but, during her lifetime, Aretha blocked its release. Whether her reasons were personal or financial, I don’t know. But I’ve seen the film twice, and it needs to be seen by millions. It brings Aretha full circle, connecting her to her roots in spiritual music, illustrating just how much she had grown as an artist -- and celebrating a voice both divine and gloriously human.

This article originally appeared in the Aug. 25 issue of Billboard.