How Judee Sill and Prince changed it all for Sufjan Stevens.

"We've, for the most part, eradicated spirituality from our lives," Sufjan Stevens says. "Religion in the past satisfied a deep desire for intimacy and sensuality in art and music. It's all very sensual when you think about it."

Religious faith and human desires are strong driving forces in Sufjan Stevens' life and work. There were two very different artists who helped him understand that the lines that divide spirituality and sensuality could be blurred.

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Judee Sill was a little known Californian singer who had a short and tough life plagued by drug addiction. When Sufjan was in high school, his step dad Lowell made him a mixtape of her music and one song has stayed with him to this day.

On 'Jesus was a Crossmaker', Judee sings about heartbreak and a lover.

"But also about religious dutifulness with the same kind of erotic passion," Stevens says.

Sufjan remembers being mesmerised and confused, not able to work out if she was singing to a saviour or a lover, as they seem to merge into the same person.

"It was dark but had a profound spiritual transcendence to it too," he says of her music.

His older sister inadvertently turned his ears onto one of the more curious tracks from Prince's 1984 classic Purple Rain.

"I remember hearing 'Darling Nikki', it has no subtlety in lyricism that Judee Sill had, but it's just beautiful in its explicitness," he says.

"It was the first time I'd heard the word ‘masturbated' in a pop song. I remember hearing that song too and being really stirred by it. It seemed so blunt and so erotic, but at the same time there's this intermix of religious kind of language.

"'Darling Nikki' is really interesting because there's like sexual erotic narrative but then there's all that reverse vocal stuff at the end of the song. If you actually reverse it, it's this little liturgical prayer in which he's singing about ‘The Lord's Coming'. When I heard that I was like that's so strange and exciting."

Hear more about the songs that changed it all for Sufjan Stevens' in this week's Don't Look Back.

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