heart and soul vs pith

heart and soul and pith both are nouns.

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

As nouns, heart and soul and pith are synonyms defined as:

heart and soul and pith: the choicest or most essential or most vital part of some idea or experience

Other synonyms of heart and soul include center, centre, core, essence, gist, heart, inwardness, kernel, marrow, meat, nitty-gritty, nub, substance, sum.

heart and soul (noun)	pith (noun)
the choicest or most essential or most vital part of some idea or experience	the choicest or most essential or most vital part of some idea or experience
	soft spongelike central cylinder of the stems of most flowering plants

heart and soul (verb)	pith (verb)
	remove the pith from (a plant)

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