When there is a speech, the speech tells a story. The person that is speaking is generally wanting the listener to have a mental image in their mind, because it strengthens what the person is saying, and it gives a good point of view on the person's speech. On the other hand, written essays are usually about explaining the details of something rather then telling it from an actual point of view. Let me know if this helps! :D
Spoken words give a look into how the characters acts. You can hear the feelings of multiple characters. Internal thoughts give you direct feelings of one character; the narrator:)
