Four short lines, and Dickinson takes the oldest story about temptation and shrinks it to the size of a kitchen garden. The claim is simple: what is forbidden tastes better than what is allowed. The poem opens on "forbidden fruit," a phrase that calls up Eden and would have been familiar to nearly any reader. It then swerves, in its last two lines, to the humblest object it could find, a pea in its pod. The central idea is that desire is created by the lock, not by the thing locked away. The poem is also quietly funny about how silly that is.
The form helps the joke along. The poem is built in the alternating long and short lines familiar from hymns and ballads. Lines one and three have eight syllables and four beats ("For-BID-den FRUIT a FLA-vor HAS"). Lines two and four have six syllables and three beats. Only the short lines rhyme, "mocks" with "locks," while "has" and "within" go unmatched. The rhyme therefore arrives late and lands hard on a closing, door-slamming sound, and the final line is the shortest-feeling of the four, snapping shut like the pod it describes. That single exclamation mark, the poem's only one, tells us the speaker is enjoying herself.
The syntax is worth slowing down for. "That lawful orchards mocks" reads at first as though the orchards are doing the mocking, but the verb is singular, so the subject must be the flavor. The grammar is inverted, with the object placed before the verb: the flavor mocks the orchards. Putting "lawful orchards" first gives them the shape of something solid and respectable, and the sentence then undermines them. "Lawful" is an odd word to attach to an orchard. It belongs to courtrooms, not trees, and it suggests fruit that is permitted, plentiful and a little dull. "Mocks" makes the forbidden flavor a bit of a bully, sneering at all the sanctioned sweetness around it.
Then comes the swerve. After the grand word "orchards," we get "the pea within / The pod," and the poem drops from a landscape to a vegetable. Dickinson then does something clever by applying "luscious," a word for ripe, dripping fruit, to a pea. The adjective is far too large for its noun, and that mismatch is the point. A pea is not luscious, but it becomes so once it is shut away. The verb helps too. The pea "lies" within, which sounds like someone reclining at ease, and a faint pun on lying is hard to ignore in a poem about temptation. The sounds link the stanza together as well: *lawful*, *luscious*, *lies*, *locks*. The repeated L lets the permitted and the prohibited echo each other, as though they were more alike than the poem admits.
The pod is "locked," not just closed, and what locks it is "Duty," with a capital D. The abstract noun becomes a jailer or a stern housekeeper with a key. This is the poem's sharpest image, because it turns the pod into a small prison or strongbox. The lock appears to make the treasure, since nothing about the pea itself has changed. Judging by the text, the poem does not say whether Duty is right to lock the pod or whether the speaker should resist. It stays with the pleasure of wanting, and the tone is wry rather than preachy.
That restraint is what makes the poem significant. It gives a whole piece of psychology in a quatrain, one that anyone who has been told "don't" will recognize. It also does so without naming a specific forbidden act, which leaves the reader to fill in their own. The Eden reference gives the idea moral weight, while the pea keeps it from becoming solemn. A small garden vegetable is made to stand in for one of the biggest stories we have, and the shrinking is where the humor and the insight come from. The poem ends by leaving the pea locked, and readers are left to notice that they, too, would rather have it than the whole orchard.