The speaker remembers being told something on a mountain: her mother taught her, through the moon, that people rise and fade like tides. It sounds like a gentle lesson about the cycles of life. Now, though, the lesson has become real. The speaker's mother lies dead, and the image of "a sliver of white" suggests both the thin crescent of a waning moon and a pale, diminished body.
In the second half, the speaker tries to give something back. She lifts the moon to light her mother's resting place, an act of tenderness and perhaps a wish to keep her close. But the moon is cold, and it burns her fingers, which hints that holding on to grief hurts. The last line, "I let her go," is short and quiet, and it feels like acceptance rather than defeat. The mood is hushed, sorrowful and calm, with love still present as the speaker lets the loss settle.