bringing it back to black music specifically and apologies if points similar to these have been made earlier
"soul" as a concept contains the idea that there's more to us than bodies
(interestingly "heart" - as a word for the center of emotion, romantic love etc - doesn't actually contain that idea: it keeps the idea of love as physiological - blood pumping, circulation speeding up in dizzy excitement - body as a hydraulic system, desire as a set of physical reactions, the chemistry between two people)
but "soul" did point to something transcending the physical - residues from gospel, Christianity etc
but some point in the 80-90s - with nu-R&B and 'new jack swing' - that reference with soul to the non-physical plane, that dropped away - it became entirely physical
a friend of mine at Melody Maker and later at Spin and Village Voice - Frank Owen, great writer about black music, hip hop, house - wrote a really good review which i don't have to hand, and can't remember what it was about specifically or where it was published (Voice? Vibe?), in which he noted how explicitly carnal and sexual the black love song had became during the course of the 90s (figures like Bobby Brown being key), and how it was no longer soul music but a pure body music - with no reference to some transcendent realm - he noted how religion-derived words had dropped out of song lyrics in R&B.
i think that shift was matched in changes in vocal style - the very last residues of raspy, gritty, Southern, Baptist cries torn from the body type testifying, these disappeared, and R&B singing become completely slick and kind of... lubricated.... a lot of legato.... slippery, slightly oily even...
before that sixties and seventies R&B had blended the two things - soul and body - that was what was radical about it - the spiritual embodied (in grand tradition of black protestant christianity in the USA - holy rollers, shaking and shimmying in the aisles, going to church as actual fun experience), the body spiritualized - the sexual act as sacred etc
hence Al Green shifting very seamlessly from singing peerless erotic-yet-ethereal songs about married love, to being the Reverend Al Green and singing of a higher love ("Belle" being a transitional moment - "you're the one that I want but He's the one that I need" - possibly misquoted from memory that)
so yeah "soul" as concept and ideal uniquely merges the earthy and the ethereal, the physical and the transcendent