Try extracting the first line from your essay paragraphs and see if you can follow your main line of argument. If you can’t, they your essay is not so easy to follow as you might want it to be. (Of course, not every argument has to be organized this way. But try to look up a few articles in some “serious” newspapers: you will find this structure widely used!)
The reason why paragraphs should be “headlined” with reference to the overall argument is to keep that argument in the reader’s mind, thereby making it easier for them to see the relevance of the rest of the paragraph. This way, the reader doesn’t lose track, and neither do you as you write.