Studying grammar gives us insight, but doesn't teach communication
Knowing grammar offers one wonderful insight into language and the human mind. It gives us the vocabulary we need to talk about how language works, how sentences are structured and how words are transformed between tenses. The inner workings of language are fascinating to English teachers, linguists, and language enthusiasts; but it is not fascinating to everyone, nor is it essential to learning how to communicate effectively. Since language learning is intuitive, students will learn best by doing, not by memorizing confusing rules and trends that an enthusiast just happened to notice.
Grammar is not just about giving insight to language enthusiasts. By understanding the inner workings of language, a student can talk about literature and writing with much more precision and clarity. It gives students the vocabulary to interpret the author's intentions, literary devices, writing style, and more in a work of literature. A student's writing can also improve by use of proper grammar mechanics and writing conventions which have been modeled in the literature that they have studied. While it is true that people acquire language naturally, to truly understand and use it effectively requires a working knowledge of grammar.
[P1] Understanding grammar can give one insights into English, but it is not essential to learning the language.
Rejecting the premises
[Rejecting P1] Grammar study is essential to learning how to properly harness the English language to communicate clearly and effectively.