In a larger sense, Hymes' claim argues that there are structures and guiding principles to which adherence is needed. The teaching of grammar, like so much in education, is something that has undergone significant revision over time. Some of the fundamental structures have been questioned or discarded. Hymes' claim reminds us that there are some specific "rules of use" that must remain with grammar instruction, regardless of climate or temperament. If these go, the claim continues, there is really no use to the discipline, as the function of rules becomes contingent and meaningless if individuals do not adhere to them. The idea of a structure and of order in teaching grammar is substantiated with Hymes' claim.
I won't write your essay, but I can give you my take on his ideas and appropriate background for support.
Dell Hymes, considered to be a "giant" of linguistics and anthropology, dedicated his life to the study of language, but not by studying the "abstract ways that people acquire grammar and other language skills" as other scholars in the field of his time. Instead, Dr. Hymes concerned himself with the basics of communication, rather than the intricacies of grammar study. Hs idea that "There are rules of use without which the rules of grammar will be useless" embraces the thought that language is dependent on more than grammar rules and structure.
In the world of linguistics, Hymes embraced the viewpoint of "communicative competence" which
involves knowing not only dictionary/grammar meaning, but also the rules that determine the appropriacy or otherwise of utterances in context.
Due to Hymes' claims, linguists began "turning their attention from language on the page to language between people" spending more time on communication rather than formal grammatical study. In other words, linguists came to a realization that the study of grammar rules alone wasn't sufficient in terms of successful communication. Hence, Hymes claim that "there are rules of use without which the rules of grammar will be useless' became the linguistic philosophy of his time.
The concept of communicative competence introduced by Dell Hymes brought about a shift in the approach method and technique in language pedagogy. Linguists argued that ‘There are rules of use without which the rules of grammar will be useless. A distinction was made between the grammatical rules that enable the users to frame correct sentences and the rules of the use of the languages to accomplish some kind of communicative purpose. Some socio-linguists rather some socio-linguistic principles became the key phrase in language teaching.