As an essay writer your main task is to research and develop a coherent argument within the quite formal structure of an essay. Grammar spelling and punctuation are extremely important when writing an essay on a subject which calls for good language skills - English Literature for example. However an essay on other subjects also needs to adhere to similar grammatical standards. The rules of grammar exist for a positive purpose such as ease of communication and to avoid ambiguity not simply for some arcane reason lost in the mists of time.
Many folks would argue that writing an essay is not the same as building a car. An essay written by one individual will always differ from that of another. Conventional Wisdom says "Essays defy standardization so of course there is no way to make writing them easy." As a result students believe that they must start from scratch all over again on each new essay assignment. The prospect causes great consternation. "What will I write? Where will I begin? If only there were some kind of essay writing system.
As any writer will know they are not the best person to look for any errors or omissions in their work. Read it through certainly pick up some obvious mistakes of course. However being too close to your writing is one of the reasons that book editors exist and of course the same applies to essay writing.