Grammatical function refers to the role of a word or phrase in a sentence. <u>Subject is a grammatical function that concerns a noun, a pronoun, or a noun phrase etc. that functions as the topic of the sentence. In other words, the subject is what the sentence is about</u>. The predicate, the rest of the sentence, will give us information about the subject.
In the sentence we are analyzing here, the grammatical function of "the idea of profit and loss" is subject, which means it is the topic of the sentence.