A lover pleads, and the harder he pleads, the colder the woman grows. Spenser turns that frustration into a puzzle of physics: if she is ice and he is fire, why doesn't the ice simply melt? The first line sets out the terms bluntly, "My love is like to ice, and I to fire", and the rest of the sonnet watches those terms refuse to behave.
The argument moves in three steps. The first quatrain complains that her cold is "not dissolv'd through my so hot desire, / but harder grows, the more I her entreat." The verb "entreat" matters. His heat is not only feeling but speech, begging and persuasion, and it backfires. The second quatrain reverses the problem. Her frozen heart fails to cool him, and he "burn[s] much more in boiling sweat," his flames "augmented manifold." The image is half romantic, half comic. A sweating lover is hardly elegant, and Spenser lets that bodily detail into the poem. The third quatrain steps back and calls the whole thing a marvel: fire hardening ice, ice kindling fire, "by wonderful device." A "device" is a contrivance or trick, so love comes across as a strange piece of machinery as well as a force.
The form helps the argument. The lines are steady iambic pentameter, and the opening line falls into its beat almost like a tolling bell: "My LOVE is LIKE to ICE, and I to FIRE." That calm regularity gives the speaker the tone of someone reasoning carefully about a scorching problem. The rhyme scheme, abab bcbc cdcd ee, links the quatrains together, because the second rhyme of each one is picked up as the first rhyme of the next. "Great" and "entreat" return as "heat" and "sweat"; "cold" and "manifold" return as "told" and "cold." The puzzle slides from one stanza into the next without a break, and the word "cold" keeps coming back, as if her chill were seeping through the whole poem. The structure of the sentences also carries the paradox. Line 10, "that fire, which all thing melts, should harden ice," puts fire, melting, hardening and ice in one breath, so the impossible happens inside a single line.
The vocabulary splits into two camps, with "fire," "heat," "burn," "flames" and "kindle" on one side and "ice," "cold," "frozen" and "congealed" on the other. Yet the camps keep invading each other. "Senseless cold" is a clever phrase. It means cold that is numb and without sensation, and it also hints at a lack of feeling in the lady. The poem never quite says whether she is cruel or simply unmoved, which keeps the speaker's frustration alive.
Three questions in a row ("how comes it," "Or how comes it," "What more miraculous thing…") give the first twelve lines the sound of a man who cannot stop asking. Then the couplet answers, or seems to: "Such is the pow'r of love in gentle mind / that it can alter all the course of kind." Here "gentle" suggests a noble, courteous mind, and "kind" means nature. Love, in other words, can overrule nature's own laws. It is a neat reply, though not a real explanation. It does not say why the lady stays cold. It renames the puzzle as a miracle, and a miracle needs no solving. The couplet also flatters, since only a refined mind is capable of such love. Judging by the tone, it keeps hope alive too: if love can make fire harden ice, perhaps it can still change her.
The sonnet is significant because it shows how much a fourteen-line poem can do. It sets out a problem, complicates it, marvels at it and closes with a tidy turn. It also shows love poetry's fondness for paradox, the habit of describing desire as a state in which opposites stop being opposites. Fire and ice are such simple images that a reader needs no footnotes to feel the clash, and Spenser's interlocking rhymes hold the contradiction together so that it reads as an argument, not just a complaint.