For that fine madness still he did retain
Which rightly should possess a poet’s brain.

Drayton invokes the long classical and Renaissance idea of poetic “furor” or inspired madness: the poet is not merely a skilled versifier but someone seized by an elevated, irrational energy that enables imaginative vision. The phrase “fine madness” suggests a paradox—madness refined into art—implying that what would be disorder in ordinary life becomes, in poetry, the very condition of creativity. By saying this “should possess a poet’s brain,” the lines also function as a normative claim about vocation: true poets retain a certain ecstatic intensity, a temperament that resists purely practical or sober-minded constraints.