heart and soul vs mental object

heart and soul and mental object both are nouns.

Word	Noun	Adjective	Verb	Adverb
heart and soul	Yes	No	No	Yes
mental object	Yes	No	No	No

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

heart and soul: the choicest or most essential or most vital part of some idea or experience
mental object: the sum or range of what has been perceived, discovered, or learned

Other hypernyms of heart and soul include cognitive content, content.

heart and soul (noun)	mental object (noun)
the choicest or most essential or most vital part of some idea or experience	the sum or range of what has been perceived, discovered, or learned

heart and soul (adverb)	mental object (adverb)
with complete faith