Differences:
1. Speeches don't need to be as structured as essays.
2. Speeches require speaking and presentation in front of an audience whereas essays are presented in written form and are supposed to be read rather than presented verbally.
3. Finally, speeches are not as formal as essays. As pointed out in #2, speeches are to be presented verbally and therefore have sayings that may not necessarily be good to put on paper compared to saying them.
For example:
People say "y'all" meaning "you all". However, writing "y'all" in an essay is not proper.
Hope this helps!
