There are two things we should consider before we begin writing an essay:
A. Subject--what is your essay about? What is the topic?
B. Meaning--what message/lesson/conclusion do you want to give to your reader?
The subject is pretty easy. You've decided on that before you ever wrote a word. I should add that there are writers who don't settle on a specific topic before they begin to write the essay. They have a kernel of a thought and off they go. If a writer doesn't consider both A and B above, the essay becomes a rambling exercise and makes little sense to anyone but the person who wrote it. However, most writers can pinpoint the topic.
The meaning is more difficult and probably more important. If you have no meaning--message/lesson/conclusion--to get across to the reader, your essay is merely anecdotal. A proper essay should have a specific message or payoff at the end.
You want to convey a universal experience or universal truth, something readers can relate to.
After you write an essay, you might want to quiz yourself with A and B above. It's similar to checking yourself on the guidelines that a particular publication gives writers. Did I do this? Did I do that? Your answers might surprise you.
Even in a personal essay, we should have some reason for writing it--a lesson, message of some kind. It doesn't always have to be spelled out word for word. Your message can be inferred. A fine essayist I know said that meaning can be implicit rather than explicit.
When you write an essay, or a personal essay, consider what it is that you want your reader to take away. What is it that you want them to remember? It isn't most likely to be the topic itself. Instead, it will be the meaning of what you've written.