The controversy over the dating, subject, and meaning of Milton's Sonnet XXIII can be resolved in the context of Milton's ideas of purification. Purification is a major theme in the sonnet, and the key to Milton's use of it is to be found in the background of the sonnet's second simile. Milton's allusion there to the rites of purification under the old law is part of a thematic pattern in which the poet progressively refers to pagan, Jewish, and Christian images of purification. The progression of these images of the dead wife returning in a dream dramatizes a purification of the dreamer's love. But the love cannot be wholly purified in this world, as suggested by the veil on the wife's face and the dreamer's inevitable awakening into darkness. This interpretation supports the traditional belief that the sonnet is to be dated after the death of Milton's second wife, Katherine Woodcock.