Every stanza of "Secret" hands the speaker something and then shows them unable to use it. They have a secret, a promise, a dream, a journey, a limit and, finally, a love. Each time, the question that follows ("who shall I tell?", "what shall it keep?") gets no usable answer. The central idea is an inward stalemate: a person full of feeling who cannot find the right listener, place or moment to put it.
The construction makes that stalemate felt rather than just stated. Each stanza is a sandwich. The opening statement and question come back word for word at the end, with a short answer trapped between them. Only the fourth stanza changes its frame, when "journey" becomes "quest". The repetition feels like a mind circling the same worry and arriving back where it started. Nearly every answer begins with "Not," so the speaker knows what will not work long before knowing what will. "Not my beloveds, / For they'll shout it loud" is half funny and half sad. The people closest to the speaker are exactly the ones who can't be trusted with the secret.
The answers also tend to slip sideways. Asked "how does it work?", the speaker replies with a place: "Not in my world." Asked "when does it start?", they answer "in my heart." The mismatch suggests someone who cannot face the question directly, or for whom feeling simply does not follow the logic of how, when and why. The dream stanza adds a pun on the word itself. A dream that exists "only in my sleep" is literal, but the line also hints at a hope that has no place in waking life.
The second stanza holds the poem's neatest paradox. A promise cannot be kept with words because "my tongue cannot speak". Yet the poem is made entirely of words. Judging by the text, the poem itself may be the one place where the unsayable gets said, a confidant who will not shout it loud. That would also answer the first stanza's question about who to tell.
The line "my love; he is elsewhere" brings in the poem's first other person, and its semicolon works like a held breath before the admission. From there the poem steers toward its last stanza. Stanza five is the only one where "Not" is followed by a firm "But." "Not on my watch, / But in my heart" is also the only place where the answer rhymes with the question, since "heart" closes on "start." The idiom "on my watch" suggests both vigilance and a clock. The limit is therefore ruled out as something the speaker controls or something time determines, and located in feeling.
The final stanza changes the verb from "I have" to "I am." Having gives way to being, and love is the one thing the speaker cannot hold at arm's length as an object. The answer, "Not with him, / But just his mind," is the most interesting line in the poem because "just" cuts two ways. It can mean "only," which makes the love smaller, a love for part of a person. It can also mean "simply," which makes the love purer, since it is a love of thought rather than of looks or presence. The speaker never settles which, and the repeated "why am I?" leaves the question open instead of resolving it.
Formally, the poem is plain. Its short lines, with two or three stresses each, and its simple, mostly one-syllable words give it the rhythm of a chant or riddle. There is no regular rhyme scheme, only quiet echoes: "keep" and "sleep," "keep" and "speak," "start" and "heart." The one noticeably longer line, "For my love; he is elsewhere," stretches out as if to show the distance it describes.
The poem matters less for any grand statement than for its honesty about being stuck. It does not pretend the speaker has solved the problem of what to do with a private feeling. It shows them listing everything they own and finding that none of it can be given away. Its repetition performs the frustration it describes, and its ending on a question rather than an answer feels truer than a neat resolution would.