Meaning: Pablo Neruda is expressing the deeper layers in everyone and everything. Including a lemon. He is illustrating how as you delve deeper you find deeper meaning and more surprising things.
Antecedent Scenario: Well if I had to make an educated guess I would say that Pablo Neruda was studying a lemon to great extend before writing this poem.
Tone: The overall tone I got from "A Lemon" was admiration and passion. Now that might seem weird to have admiration for a lemon but what I believe Pablo Neruda was going for was the lemon's great qualities and how it can be applied to everyone and everything.
Agency: The main agent in this poem is the lemon. The lemon does not change throughout the poem. The lemon only gets described in more detail as the poem progresses.