Most people expect heaven to be a reward waiting at the end of a long journey. Emily Dickinson's four lines turn that expectation upside down. Her claim is that heaven is something you must learn to find here, and that if you can't, you shouldn't expect to find it later. Anyone who "has not found the Heaven -- below --" will "fail of it above." The second half of the poem explains why, and it does so with a surprising, almost comic picture: angels live right next door, "Wherever we remove."
The poem is built like a proverb. It opens with a "Who" clause that acts as the subject of the whole sentence, and the verdict doesn't arrive until the next line. That gives the stanza the feel of a warning, or a rule of thumb passed from one person to another. The verb "fail" carries a faint note of examination, as if finding heaven on earth were a test whose results are carried forward. The words "below" and "above" sit at the ends of lines one and two, facing each other like the two halves of a scale. Yet the usual order is reversed. Heaven is named first and "below" comes right behind it, so the two words are joined before the poem has taken a breath. Dickinson's dash after "below" then holds the reader there, in the lower world, for a moment longer than is comfortable.
The imagery is where the poem becomes unusual. Dickinson explains a point of theology with the vocabulary of house-hunting. Angels "rent the House next ours." Renting is an ordinary, slightly unglamorous activity. It makes the angels tenants, not rulers, and it suggests they have simply taken a place on the same street as us. The capital letters on "Angels" and "House" lend them a little dignity, but the idea behind them is humble. The final word, "remove," is used in the older sense of moving house. It also means taking something away, which is exactly what the poem says we cannot do. We can change address as often as we like, but the neighbours move too. Reading the poem as a joke about the impossibility of escaping heaven is, I think, fair. The tone is wry, even playful.
The sound of the stanza supports this gentle tone. The lines alternate between eight and six syllables, the pattern of the old hymn and ballad stanza, which would have been very familiar to a reader steeped in church music. The beat is a steady, easy iambic one, and the short second and fourth lines land like firm closing statements. The rhyme is where Dickinson bends the form. "Above" and "remove" look like a pair on the page, but they don't quite sound like one. The eyes expect a match and the ear is left slightly unsatisfied. That near-miss suits a poem about something close at hand that is easy to overlook. The first and third lines don't rhyme at all, so the stanza has only a loose grip on its own music, much as its argument loosens our grip on the usual picture of the afterlife.
The poem's quiet cleverness is that it never says what the "Heaven -- below --" actually is. It could be love, nature, friendship, a good day, or simply attention to the world. By leaving the term open, Dickinson makes the reader supply it, and that is the lesson in action: you have to recognise your own heaven, and nobody can hand it to you. The suggestion is that the angels are already close, and the one thing missing is the ability to notice them.
That is why such a small poem is worth reading closely. In a few lines it shows several habits that make Dickinson's writing recognisable: compression, odd capitals, dashes that act like breaths or hesitations, a slant rhyme, and the way she brings huge subjects down to household size. Heaven and eternity are explained through the next-door house, which is not a diminishing of the subject. It insists that the eternal is not far away, and that the ordinary street is the place where the test is set.