Look up the word “sentence” in the Oxford Unabridged Dictionary, and you might be surprised (as I was) how, over the years, the word has been used, and the historical range and complexity of its various meanings has changed.
That said, the definition that interested me the most was “Sentence: The thought or meaning expressed, as distinguished from the wording; the sense, substance, or gist (of a passage, a book, etc.).” What struck me here was that following this definition, came the letters, “Obs.” That is to say, this usage is considered obsolete. Yet I suspect it is this meaning good writers have in mind when she/he writes a sentence: that is, a sentence—at its best—expresses something beyond the words themselves. It constitutes the classic, “Show, don’t tell” ideal. It may be a bit of dialogue. It may be a line of detail, or some brief exposition. Beyond all else, It reveals thought or meaning, as distinguished from the wording.
We tend—as writers—to focus on plot, ideas, conflict, etc. The sentence is, I think, worth much thought and time. Think of a good sentence as a bright star in the sky of your writing. It does not just stand out; it is what makes literature shine.