"Let the Light Enter" by Frances Ellen Watkins Harper has a fairly simple rhyme scheme. The structure of the poem is six stanzas, each of which are four lines. In the first stanza, Harper employs an abab rhyme scheme, but abandons this by the second stanza, only choosing to rhyme the second and fourth lines.
The poem has what I would consider to be a trochaic rhythm. A trochee is a metrical foot consisted of a stressed syllable followed by an unstressed syllable -- the opposite of an iamb. If you recite the poem aloud, you will hear, from the first word, "Light!," that Harper begins with a sound that lifts, followed by a sound that falls. A trochaic rhythm is also called a "falling rhythm," which suits this poem about death.
Now, let's consider the figurative language that is used. In the first stanza, Harper likens life to water. Water is fickle and evaporates; so, too, does life. Goethe's life is "ebbing low," like a sea at low tide. He wants to throw open the windows and let in more light so that the shadows can "deepen." "Deepen" can also refer to the contrast between dark shadows, reminding one of shades from the underworld, and the light from the sun, or of Heaven.
The speaker's senses continue to shift from the earthly world to the heavens. The light is "balmy," a word that we associate with summer heat. Both the sun, which "[plays]," and his "bed," which is "dying," are personified. He identifies with these objects that he will soon leave behind to enter "the dimly lighted valley," which he "with lonely feet must tread."
In the third stanza, Death enters the room and it, too, is personified. It "[weaves] shadows 'round [his] waning sight." There is a bit of alliteration with "weaving" and "waning."
The first two lines of the fourth stanza apply a bit of anaphora -- that is, the repetition of a word at the beginning of successive clauses or sentences for emphasis. "Not" is repeated to emphasize the simplicity of the poet's needs. He no longer has use for genius or grand thoughts, simply "more light."
In the fifth stanza, the ephemeral and pointless nature of fame is emphasized. Because the poem is about the death of Johann Wolfgang von Goethe, Germany's greatest poet, the meditations on fame and genius are significant. Harper employs inversion in the first line: "Heeds he not the gathered laurels, / Fading slowly from his sight..." "Laurels" are associated with praise and accolades, none of which he can remember, none of which matter on his death bed when he merely wants to live: "All the poet's aspirations / Centre in that prayer for light."
The sixth stanza makes an appeal to a "Gracious Saviour." "Life's day-dreams" materialize, then "melt and vanish from the sight." This image reminds one of snow or ice melting. Our dreams congeal like ice; they become fixed and immutable during life, but disappear just before death. We cannot remember them; they do not matter. "Our dim and longing vision" is for "light, more light." "Dim" implies that life is fading. In death, it is said that things are getting dark. However, the passion to live does not fade, there is "longing."
One could read the last line as a wish to be delivered to heavenly grace, as there is an appeal to a "Gracious Saviour." However, I read it as a longing to live just a little longer. The desire for "light, more light," "earthly light" from the "balmy sun" indicates that the poet wants to stay on earth longer, and is not eagerly seeking the afterlife.