Four short lines, and a definition that cancels itself out: that is the trick Emily Dickinson plays here. Asked what beauty is, the speaker replies that the question has no answer ("That Definition is none"). Instead of apologising for the failure, the poem treats it as proof.
The syntax is knotty, so it helps to untangle it. The most natural reading is that beauty's only definition is a definition "Of Heaven," one that eases or relieves analysis, "Since Heaven and He are one." Who "He" is, the poem never says. It might be Beauty personified, or it might be God. Both readings end up in the same place. Beauty is not something to be taken apart and labelled, because it is bound up with the divine, and the divine cannot be separated into pieces.
The construction enacts this idea. The first line ends on the small, weak word "is," and the sentence hangs there, promising a definition. Line two swerves away and the promise collapses. The word "Definition" appears twice, first as something expected and then as something denied, so the poem seems to circle back on itself rather than move forward. Even the phrasing "Definition is none" is slightly twisted. Ordinary English would say "there is no definition," but the inverted wording makes "none" land with a thud at the end of the line, like a door closing.
Sound reinforces meaning. The rhyme scheme alternates, and the second pair, "none" and "one," is a full rhyme. The two words are also nearly the same word: "none" is simply "one" with an extra letter in front. A single letter divides nothing from unity, and that is the poem's argument in miniature. Where no definition exists, oneness takes its place. The first pair, "is" and "Analysis," rhymes much more loosely, since "Analysis" ends on an unstressed syllable that only half-echoes the short "is." That looseness suits a line about analysis being eased. The rhyme itself feels relaxed and not tightly screwed down.
Dickinson's word choices are worth a closer look. The big abstract words, "Definition" and "Analysis," are long, Latinate and slightly clinical. They are the vocabulary of a classroom or a laboratory. The words that overturn them are tiny: "none," "one," "He," "Heaven." The poem lets the heavy, technical vocabulary pile up in the first three lines, then dissolves it with plain monosyllables in the last. "Analysis" comes from a Greek word meaning a loosening or untying, so "easing Analysis" is almost a pun. The thing that normally unties ideas is itself being gently untied.
The little word "Since" matters too. It gives the final line the sound of a logical proof, as if the speaker were closing a tidy syllogism. But the conclusion of the argument is that arguments are unnecessary. The poem borrows the manner of reasoning in order to point beyond it. The capital letters on Beauty, Definition, Heaven and Analysis add to the effect. In this printing they turn abstractions into something like characters, each with its own weight, and set them in a quiet drama in which one of them, Analysis, is politely sent out of the room.
The poem is significant for exactly this reason. It is a piece about the limits of explanation that refuses to be fully explained. Anyone writing about it quickly feels the irony: every attempt to define what the poem says repeats the gesture it gently mocks. Dickinson's compression is typical of her short poems, where a great deal is packed into a handful of lines, and here it makes a large claim about aesthetics and faith in under thirty words. The poem does not tell us what beauty is. It makes us feel the point at which telling stops, and it suggests that this point is where beauty begins.