Dickinson structures the poem as a contrast between two baptisms—one performed on her as an infant ("without the choice") and one she's performing on herself "consciously." The first eight lines inventory what she's discarding: her baptismal name, her dolls, her spools of thread. These aren't random objects—they're the apparatus of 19th-century female childhood and domesticity.
The turn happens at line 8: "Baptized before without the choice, / But this time consciously." The second baptism isn't Christian—there's no church, no water, no congregation. It's a self-coronation. The "supremest name" she's baptized into is never specified, which is the point. She's claiming the right to name herself.
The moon imagery tracks her growth from incomplete to whole. "Crescent" is the waxing moon, partial and still forming. When she drops the crescent, "Existence's whole arc" fills up—she becomes the full moon. The "diadem" (crown) is small because it's complete, not because it's inadequate. A full moon is smaller in the sky than a crescent arc, but it's whole.
The final stanza makes the power shift explicit. As an infant, she was "crowned, crowing on my father's breast"—note the pun on "crowing" (both crying and being crowned). She was "half unconscious," a "queen" only in potential. Now she's "adequate, erect, / With will to choose or to reject." The poem ends with that choice: "just a throne." Not the crown someone places on you, but the throne you claim for yourself.