Is the phrase ‘serve you heart and soul’ grammatical? And what does it mean?
If the phrase becomes ‘serve your heart and soul’ or ‘serve you with heart and soul’, does it still make sense and what meaning does it carry?
We have several expressions and collocations that function even when they lack a preposition to define how the second noun phrase relates to the first one.
For instance, wait on (someone) hand and foot is well attested. Merriam-Webster defines the idiom:
: to provide everything that someone needs or wants : to act as a servant to (someone)
Sure, for technical clarity one could add a preposition like with, but it breaks the immediacy of the idiom. Instead, "hand and food" has an adverbial sense to it even without the preposition, as it explains the manner in which someone performs an action:
She waited on her children hand and foot.
She waited on her children with hand and foot.
Similarly, heart and soul is a common expression. It can serve as a noun phrase ("My heart and soul went into this"), but in this instance it is an adverbial meaning completely or wholly. If one puts their heart and soul into something, they are putting everything important into it. Again, Merriam-Webster:
: without reservations : completely, wholly count on me to help heart and soul
Merriam-Webster claims this is an adverb. Adverb, adverbial - when used with verb phrases that take an object, heart and soul modifies how the verb should be understood. So the expression can be used with several verbs:
His first letters from there are very contented and he devotes himself heart and soul to his work, especially the practical part of it ... (The Letters of Vincent Van Gogh, 2011)
That gentle Palamon, your own true knight, / Who loves and serves you, heart and soul and might (Canterbury Tales, trans. Nevill Coghill).
In her mortification Varvara Petrovna threw herself heart and soul into the “new ideas,” and began giving evening receptions. (Complete Novels of Fyodor Dostoyevsky (Unabridged), trans. Constance Garnett).
Similarly, serve you heart and soul means to serve you wholeheartedly or wholly.