This is a Petrarchan sonnet. The rhyme scheme for those usually is ABBA ABBA CDCDCD, or CDECDE. The first eight lines are called the octet, and the last six are called the sextet. However, in this sonnet the sextet goes CDCDFF. This is a very creative ending as it allows the sonnet to end in a couplet.
The final line, too, is unusual, because it has six iambs instead of the traditional five. However, the poet knew what he was doing. A normal couplet, "For thy sweet love remembered such wealth brings That then I scorn to change my state with kings," "My words fly up, my thoughts remain below. Words without thoughts never to Heaven go," "For I have sworn thee fair, and thought thee bright Who art as black as hell, and dark as night," because of its pentameter rhythm, sounds final. The Petrarchan ending, the sextet, because it does not have any couplets, sounds less final: "For I am brimful l of the friendliness That in a little cottage I have found; Of fair-haired Milton's eloquent distress, And all his love for gentle Lycid drowned; Of lovely Laura in her bright green dress, And faithful Petrarch gloriously crowned."
This lesser sense of finality causes the end of a sonnet to seem more "open." In the current sonnet, the end is even more open. Though the final two lines rhyme, the last iamb is the sixth, and not the fifth. This "skips over" the fifth iamb, and though the reader knows he is finished at the sixth, the sense of finality is almost completely avoided. Nothing else, of course, would have been appropriate for such a line.
In the octet, the poet rejects a Romance so that he may concentrate fully on King Lear. He tells the Romance to "Leave melodizing on this wintry day," this implies that a Romance, something fair and light, is not appropriate for winter. The imagery here is two-fold: first, the Romance reminds one of spring, and love, and roses, and frilly things like that which all belong to spring, which is the better season in which to enjoy a Romance. The second is that of winter: the storms, the cold, and the barren landscape. These evoke the image of the heath, and the storm which drives Lear mad. The dead of winter, when the elements are closest, is the most appropriate time to read King Lear.
The poet calls King Lear, "The fierce dispute Betwixt damnation and impassioned clay." This sounds like one of the more accurate descriptions that I have hard but it is still difficult to discover exactly what he means. Presumably "impassioned clay" is the existence Lear is living at the moment. We are but clay that has been endowed with passions. When we die, we return to dust, and our passions are lost. However, if one has a spirit that lives on, it might go somewhere else. Here, the only other end for that poor soul is damnation. Either one lives eternally in pain, or one lives impassioned, and then doesn't live at all. I don't think Keats means that Lear is unsure what would happen to him after his death. Rather, that Lear's battle with his daughters, and with the elements on the heath, are the dispute, and the only outcomes of this dispute are damnation or to become impassioned clay. This truly is a tragedy; the hero will fall, and can in no way save himself. Damnation, here, is madness. Lear's mind is "damned" because he is no longer its master. The clay is Lear's dead body. Lear must either be mad, or dead.
Final four lines are somewhat difficult. What is the old oak forest that leads to the barren dream, and what is the consuming fire? Perhaps the old oak forest is the forest through which Lear traveled to get to the heath, and the heath, the location of the height of Lear's terrible madness—most terrible here, because he is still sane enough to understand what is happening—is the barren dream. The poet is asking the Bard and the "clouds of Albion"—of England—to help him avoid the same fate as Lear. He seems to be saying that such a fate is unavoidable. When this happens, please secure my fate. The fire is possibly the madness and overwhelming nihilism from which Lear suffered. Perhaps in this way such a fate is unavoidable. Not everyone will be unloved by his dragon daughters, but perhaps at some point everyone becomes mad and, like Lear, calls for the heavens to fall:
"Blow winds, and crack your cheeks! Rage, blow, You cataracts and hurricanoes, spout Till you have drenched the steeples, drowned the cocks! You sulphurous and thought-executing fires, Vaunt-couriers to oak-cleaving thunderbolts, Singe my white head; and thou all-shaking thunder, Smite flat the thick rotundity of the world, Crack nature's mold, all germens spill at once That makes ingrateful man."
When this fire comes on Keats, he asks that he does not suffer and continue as Lear, but that he may rise like the Phoenix
from the ashes of his mind.
The sonnet captures very well both the passion of King Lear, and of the poet's response to the play. It is almost amazing how much a poet can pack into a mere fourteen lines, but these fourteen lines contain a whole reading of King Lear.