Drayton starts by insulting his reader. "Thou leaden brain" is a startling opening for a love sonnet, a form that usually flatters a mistress rather than abuses a critic. Someone has called his lines "dull" and said they do not "move," and the speaker answers with a shrug of contempt. Of course you feel nothing, he says, because you have never felt my "fiery touch of love." Lead is heavy, grey and cold, so the insult turns a literary opinion into a fact about material. The critic's mind is made of the wrong stuff to catch fire, and the poem's whole argument about fire and refinement grows from that first word.
At "But thou" in line five, the address seems to change. Judging by the sense of the lines, the lead-brained critic is left behind and Drayton turns to a different reader, one who knows love from the inside. What follows is a catalogue of that person's suffering, and it is not pretty. The pen has worked "like a pack-horse," so love-writing is drudgery rather than inspiration. The stomach has turned food "to gall," bitterness made literal. The senses are "poor prisoners, hunger-starv'd," and grief has "parch'd" the body and "dried" the blood. The images move steadily inward and downward, from the pen to the stomach to the senses to the blood, as though the lover were being emptied out from the hand to the veins.
The third quatrain moves from physical decay to emotional chaos. The lover has "scorned life and hated death," and in one moment is "mad, sober, glad, and sorry." That line runs to eleven syllables and ends on a weak extra beat, and the overflow suits the jumble of moods it describes. The pairs of opposites echo the contradictory feelings familiar from the sonnet tradition, but here they read less like polite ornament than like a symptom. The mention of Purgatory sharpens the picture. The lover has endured "thousand plagues, more than in Purgatory," and Purgatory is a place of suffering meant to cleanse. That prepares the key verb of the couplet, as Love "in his fire refines" the spirit. The poem has moved from lead to something like refined metal, and the imagery suggests that pain is the furnace that purifies.
The syntax is where Drayton shows his craft. The sonnet follows the Shakespearean pattern of three quatrains and a couplet, rhymed abab cdcd efef gg, in iambic pentameter that is sturdy enough to carry the angry opening. Some pairs, like "move" and "love" or "food" and "blood," match on the page even if modern ears hear them differently. From line five onward, though, the poem is one long sentence built from piled-up clauses: "whose pen," "whose stomach," "whose senses," "whose grief," "thou which," "thou which." The main verb is held back until the very last line, when it finally arrives as a command: "Come thou, and read, admire, applaud my lines." The accumulated pressure of ten lines releases in one sweep. The three verbs also escalate, from reading to admiring to applauding, so the speaker moves from asking for attention to demanding a standing ovation.
There is a paradox at the heart of the poem. In line three the speaker mentions his "delight," yet everything he describes afterwards is misery. The sonnet suggests that for the true lover the two are inseparable, and that the starved, parched, half-mad state is the delight. That gives the poem a defiant, slightly comic swagger, but it also makes a serious claim about reading. Only someone who has been through the fire can judge what the fire produces.
This is what makes the sonnet worth studying. It is a poem about its own audience, and it sorts readers into those with leaden brains and those with refined spirits. Instead of pleading for approval in the courtly manner, it sets experience as the test of taste and dares the reader to pass. Whether or not we accept that only the heartbroken can judge love poetry, the poem is vivid proof of how a sonnet can use argument, insult and a long-delayed verb to turn a complaint about critics into a portrait of love as ordeal.