«My love is as a fever, longing still
For that which longer nurseth the disease».
The final sonnets concerning the mistress, beginning with this one, return the poet to the disturbed state of previous sonnets.
My love is as a fever, longing still
The image of feeding in Sonnet 146 continues in Sonnet 147, only now the feeding is not on death but on illness, and there is no possibility of immortality from lusting after the mistress: “My love is as a fever . . . / . . . / Feeding on that which doth preserve the ill, / Th’ uncertain sickly appetite to please.” Completely apparent is the poet’s inability to separate himself from the relationship.
The poet’s reasoning completely fails him. Reason, in the form of a physician, has left him because it can do nothing more to save him from the despair of loving the mistress. Again he acknowledges that his soul’s immortality is beyond reach: “Desire is death. . . . / Past cure I am, now reason is past care.” His thoughts now move madly, expressed in such terms as “frantic mad,” “evermore unrest,” “madmen’s,” and “At random.” Despite his ability in the concluding couplet to differentiate between his expectations of his relationship with the woman and the outcome of that relationship, his despondent tone indicates that he is too far gone ever to regain self-confidence.
English audio from YouTube Channel Socratica
Summary from Cliffsnotes.com