The world Rossetti writes about is to be understood in a Biblical context: it is what obscures the real heavenly truth, what makes one stray from redemption. Yet, especially in the Romantic tradition, it is precisely through encounter with and existence in the world that poetry is born. The double, almost paradoxical meaning is expressed in the title and developed throughout the poem.

The text consists of a series of dichotomies between night and day, desire and love, decay and health, monsters and saints, death and life. They embody, respectively, corruption and redemption.

Beyond the rather obvious religious reading of the poem, and because of the paradox set up by the title, it is possible to read it as an allegory for the poet's lot: poetic inspiration is elusive, shifty, can lie and obscure, but it is also a way to access truth.