The poem sets two kinds of light against each other: the small, flickering light of a candle and the huge, free light of the sun. At night the flame makes shapes out of shadows, a kind of private, half-imagined world. But the wick is burning out, and as it fades the sun comes up. Something bigger and better has arrived, quietly and without effort.
The last two lines turn to "you," and the tone shifts. The speaker says this person's eyes were "closed so tight" that they never noticed the daylight. The word "tight" suggests the blindness isn't an accident. It feels like a choice, or a stubborn refusal to look.
The speaker seems frustrated, maybe a little sad, watching someone miss what's right in front of them. The mood is calm on the surface but carries a quiet sting, helped by the neat rhyme of "tight" and "light," which closes the poem with a sense of disappointment.