the last lines are put in a bracket because they do not make the thoughts of the poet, and neither do they make the voice of the rain. What they contain, is the observation that the poet made as regards the course the poem is taking.
b)
reck'd or unreck'd means that whether or not you cared for the sound of the rains, if someone listened to the sound made by the rain, if someone didn't listen, whatever the case may be, it does not affect the rains and neither does it affects the poet.
