I need to define what is the difference between essay and letter writing. Preferred is the answer with good examples.
Those are two completely different types of writing due to several reasons.
#1. Style of writing
While letters are more of a conversational and informal style; an essay requires you to follow academic style.
An essay always requires thorough investigation done before writing. A letter does not.
An essay is usually divided into three parts, namely Introduction, Body and Conclusion, with a due specific of each of them.
A structure of your letter depends on whether it is formal or private. Private letters don’t have any required structure, while official letters do have.
An essay is usually written to express a point of view on the issue, analyse the information, use facts to convince readers in your point of view.
A letter might serve several purposes. It can inform, request, explain, remind of something, etc. Also depends on whether it is private or formal.
The essay is written to be read by multiple people, who most certainly would evaluate it. Those people are usually not related to the sender or the issue he writes about.
A letter is written to one person, organisation or a specific group of people, who are related to the sender.
If I missed something, feel free to continue the list below in own comment.