This poem is set in high summer and tells the story of a secret lovers' tryst. As Emily Dickinson’s love interests at the time were married men we can assume that this is the scenario she is describing. However, it can be dangerous to make assumptions about a biographical application; this could be a work of imagination.

During their brief time together the lovers pledge
that they will meet in heaven and enjoy eternal marriage. This will be their reward for their present suffering on earth.

The setting is an appropriate backdrop to their feelings. Summer is characterized by impermanence; the growth and lushness is fleeting and will soon be lost.

There came a Day-at Summer's full, — Bloggingdickinson

The summer solstice is the peak of summer in solar terms: it's the longest day of the year. Coming in June, it also coincides with beautiful bloomings, birds, and butterflies. Add to that a rendezvous with a secret lover and what could be more perfect?

Structure
The poem comprises seven quatrains or four-lined stanzas. The story progresses from description of the summer countryside, the lovers' relationship, their meaningful silence, and when their time together is over their pledge to meet in heaven — the reward from the “Calvaries of Love”.

There is a regular ballad or hymn structure, with an ABCB rhyme scheme. The metrical rhythm is iambic tetrameter (four iambs or metrical feet per line) alternating with iambic trimeter (three iambs or metrical feet per line), where a iamb is a metrical foot made up of one unstressed followed by one stressed syllable.

Language and Imagery
The voice is that of a first person narrator, who may or may not be the poet. However, it is possible that Dickinson drew to some extent on her own experience.

The narrative is divided into the poet’s characteristic style of short, choppy phrases and frequent dashes that form caesurae or pauses that suggest the reader is party to the poet’s thoughts as they occur to her.

The poet’s love story is deeply interwoven with religious references. The setting in high summer is, for example, the “Wardrobe of our Lord”. The poem begins with a reference to the “Saints” and ends with a marriage in Heaven, a reward for the “Calvaries of Love”. The detailed annotations provide deeper analysis.