stuff vs heart and soul

stuff and heart and soul both are nouns.

Word	Noun	Adjective	Verb	Adverb
stuff	Yes	No	Yes	No
heart and soul	Yes	No	No	Yes

As nouns, heart and soul is a hypernym of stuff; that is, heart and soul is a word with a broader meaning than stuff:

stuff: a critically important or characteristic component
heart and soul: the choicest or most essential or most vital part of some idea or experience

Other hypernyms of stuff include center, centre, core, essence, gist, heart, inwardness, kernel, marrow, meat, nitty-gritty, nub, pith, substance, sum.

stuff (noun)	heart and soul (noun)
miscellaneous unspecified objects	the choicest or most essential or most vital part of some idea or experience
unspecified qualities required to do or be something
a critically important or characteristic component
senseless talk
information in some unspecified form
informal terms for personal possessions
the tangible substance that goes into the makeup of a physical object

stuff (verb)	heart and soul (verb)
fill with a stuffing while cooking
fill tightly with a material
treat with grease, fill, and prepare for mounting
overeat or eat immodestly; make a pig of oneself
cram into a cavity
obstruct
press or force

stuff (adverb)	heart and soul (adverb)
	with complete faith