When building a city, you have to look at it from a distance. You can't be close, because you will only see your house. But looking from above, we can see if the streets have been mapped out right or if the houses are too close. Only from above can we see if all the intricate, little patterns in each house, roof, street, business, park and so on fit together in the working machine of a city.
But we won't know if the city really is planned right unless it's lived in.
When writing, we can edit as soon as we finish, looking from above, but our stories haven't been 'lived in' yet. We still have the 'missing pieces' from our story in our minds. We fill in blanks without realizing it and pass over blatant errors, thinking we remember why we wrote that particular line. When you take at least a few months before you do your final edit, you won't remember everything. The writing becomes... fresher.
When you look at something with clean eyes, from a far distance, you can see glaring holes. It allows you to look close at a building and ask, "Why this color?" or pan back and pick apart the highway. In our writing, it lets us see how bad some of our work really is. We find what our weaknesses are, and we can become mindful of them--making our newer work much easier to read and edit.
After letting the story feel 'lived in,' we can see the missing errors or plotholes. We can make sure to show, not tell with some villainous monologue left for the ending.
Time, in editing, is distance. Give yourself distance, and you'll have the best chance of being published. The publishing world will still be there tomorrow. If we want to show how brilliant our writing is, we must first be wise beyond our years.