Nightfall in Longfellow's poem is less a mood of gloom than a changing of the guard. The "little moon" sinks "silently, / All silently," and the repeated word hushes the sky, as if the stage were being cleared. What remains is "the cold light of stars," and the first to take command is Mars. The phrase "the first watch of night is given" turns the heavens into a military post, with the red planet as sentry.
The poem then stages a small argument with itself. The red glow might suggest romance, and the speaker asks, "Is it the tender star of love?" The answer is an abrupt "O no!" The sky becomes a "blue tent," a camp, and what shines in it is "a hero's armor." From here the imagery is all equipment: a shield, a "mailed hand" that beckons. The speaker stops being a passive stargazer and becomes someone being addressed. The star "smile[s] upon my pain," and the speaker is "strong again." The poem never says what the pain is, which lets almost any reader step into it.
The most interesting design choice is the echo between the second and sixth stanzas. Both end with the first watch of night and Mars, but the grammar shifts. "The first watch of night is given" becomes "I give the first watch of the night." The same applies to the light. In stanza two there is no light "in earth or heaven," while in stanza six there is none "within my breast." The darkness outside has moved inside, and the speaker now takes up the sentry's duty himself. Then the star itself rises in the breast, personified as "he," and the adjectives pile up: "Serene, and resolute, and still, / And calm, and self-possessed." The repeated "and" slows the line until the stanza almost enacts the stillness it describes. There is a pleasing paradox here too. Mars, a name tied to war, ends up teaching composure. The strength on offer is not aggression but the "unconquered will."
The form supports this steadiness. There are nine quatrains rhymed ABAB, with long lines of four beats alternating with short lines of three, a pattern familiar from hymns and ballads. The poem even calls itself a "brief psalm." Most rhymes are plain and sturdy (soon/moon, love/above, stand/hand), though a few, like pain/again, rhyme more neatly in some pronunciations than in others. The simple, regular beat makes the lines easy to remember and gives the poem its calm authority.
In the last two stanzas the poem turns outward. "Whosoe'er thou art, / That readest this brief psalm" pulls the reader into the scene, and the line "As one by one thy hopes depart" seems to lose something with each beat. Then comes the closing advice: "O fear not in a world like this." The final phrase is "To suffer and be strong," and the word "and" matters. Strength does not arrive after suffering is over. The two exist together, and that is what the poem calls "sublime." The word "erelong" makes this a promise to be discovered over time, not an instant cure.
The poem is significant for how it reworks a familiar subject. Stars in poetry often stand for romance or distance, and Longfellow deliberately refuses the first of these. He makes a red point of light into a model of endurance, and he states his moral plainly instead of hiding it. Some modern readers may find that too tidy, but the clarity seems to be the point, since the poem is built to be carried in the memory. It leaves a question worth debating: is the advice to "suffer and be strong" a comfort, or a demand?