You should be able to state it in one of two sentences. The purpose of your essay is to explain this idea. Each paragraph should have its own main idea, one that supports the paper's thesis. Each paragraph is about one part of your essay topic, and should make a statement about that part and explain it, giving examples. The meaning of every sentence must be clear.
Sentences can be free of grammatical errors and still be confusing.
Good writing is clear, not fancy. The best method of checking for clarity is to read your paper out loud slowly, and to hear it read out loud to you by someone else. To see if your essay is well-organized, try to outline it. If the idea expressed in a short paragraph can't be combined with another paragraph or expanded into a longer one, consider the possibility that it should be left out. Generally, it is best to present the strongest evidence for your point last.