The world will little note, nor long remember what we say here, but it can never forget what they did here. What Rhetorical Device is this and why?

The rhetorical device used in this passage is antithesis.

Explanation:

Antithesis is a rhetorical device that achieves a contrasting effect by putting two opposite ideas together. Antithesis uses word parallelism so that the contrasting words, phrases, or ideas present similar grammatical structures.

The passage we are analyzing here is an excerpt from Lincoln's famous "Gettysburg Address." The first idea is that what he says is insignificant and will soon be forgotten. The second idea is that the death of soldiers during the Civil War will never be forgotten. Notice how one thing will not be remembered while the other will, and how they are placed side by side. This is a beautiful example of antithesis.

where is the writing? (so i can answer)

rising action   i think i did this not sure