Question

Why are the last 2 lines of the poems written in brackets?

Answer 1

The last two lines are written in brackets because those two lines are the thought of the poet, while the entire poem talks about what the rain is saying.

Hope this helps..!!

Answer 2

In English, parenthesis (which I learned (from a comment) is what this question is really asking about) indicate an aside--a sidetrack from the main point the sentence is making. In most cases, you could remove the parenthetical phrase and the sentence would still make sense: "In English, parenthesis indicate an aside--a sidetrack from the main point the sentence is making."