The speaker sees the moon as something that protects and comforts. Each stanza gives it a new job. First it's a flashlight, something practical that helps a person who is lost at sea find their way. Then it becomes a mother's eyes, left in the sky to watch over her children while they sleep. After that, it's a light that chases away the monsters under the bed, which fits a child's way of thinking about the dark.
The last stanza shifts from comfort to admiration. The moon is a bright pearl, and its beauty is reflected in the sea, which the speaker calls a "sea of mirrors." The mood is gentle, safe, and a little wondering, like a bedtime thought. The speaker clearly feels grateful to the moon and trusts it. The simple comparisons make the poem feel childlike, and the moon seems like a kind presence who is always there when things feel dark or frightening.