"Life of the mind" is the phrase we use for scholars and philosophers, and the poem answers it with a child's version: a secret, a few books and a missing doll. The gap between the grand title and that small inventory is where the poem lives. It is about a solitary inner life, about how it grows out of loneliness, and about how it seeps outward until ordinary perception slips slightly out of true.
The first couplet sets the terms. "A secret was her only company" makes an abstraction into a companion, and the flat verb "was" and the word "only" tell us how bare her days are. Then the line breaks and the books arrive almost as an afterthought: "that and her books." The second line is shorter than the first, so the books seem to shrink into second place. The secret is never named. The poem keeps it from us, so we are placed among the people who are shut out of her private world.
The second couplet brings in the doll, and with it the voice of other people. "Her doll is gone away to live / (they say) in the country" sounds like what adults tell a child when something has quietly disappeared. The line break leaves "live" hanging at the end of the line, and the parenthesis "(they say)" immediately undercuts it. We hear a comforting story and the speaker's doubt about it together. Judging by the order of the stanzas, the doll's departure may be what leaves the girl with only her secret, but the poem doesn't say so. It sets the two facts side by side and lets us draw the link. Because the doll is a toy, we can reasonably infer a young girl, though the text never states her age.
The last couplet shifts suddenly to "we." "So buying a rose we mistake it / (strange fancy) for a bell." The little word "so" pretends to introduce a consequence, but nothing in the earlier lines causes this. The logic is that of association or dream. The speaker has also become part of a group, and one reading is that the girl's private, slightly unreal way of seeing has spread to everyone. Another parenthesis, "(strange fancy)," matches "(they say)." Both are the poem's quiet asides, and in both the voice steps back to comment on itself. The rose and the bell cross the senses. A rose is silent and meant to be looked at and smelled, while a bell rings, calls and perhaps mourns. To mistake one for the other is to hear what should only be seen, which is the kind of slip a mind makes when it lives too much inside itself.
The form is spare and fits this material. There are three unrhymed couplets, no capital letters, and no punctuation except the two parentheses. There is no full stop at the end, so the poem trails off instead of closing. In each couplet the second line is shorter than the first. The first couplet runs seven syllables, then four. The second runs seven, then six. The third runs eight, then six. Each stanza ends with a drop in length, like a breath let out or a door pulled almost shut. The rhythm stays close to speech. "So buying a rose we mistake it" tumbles forward on its unstressed syllables and then stops at the single heavy syllable "bell." It is the last word of the poem, and it works as a sound that lingers after the poem ends. The b of "books" and "bell" also faintly links the first and last couplets, as if the girl's reading and the strange ringing belong to the same world.
The poem's significance lies in how much it does with so little. In about thirty-five words it suggests a whole situation: a lonely girl, a loss softened by evasions, and a world that begins to blur at the edges. It never explains any of this. It trusts the reader to feel the pressure behind the plain statements, and that gives the title its irony. The "life of the mind" here is not grand intellectual work. It is what a mind builds when it has only a secret and some books for company, and the poem suggests that this kind of inner life can be both sad and quietly inventive.