This poem takes the form of a sonnet, although not a typical sonnet. It mixes both the Shakespearean sonnet and the Italian sonnet. A Shakespearean sonnet's rhyme scheme is abab cdcd efef gg. An Italian sonnet has an octet first, with the rhyme scheme abbaabba; then, the sextet can be any rhyme scheme but cannot end in a couplet. As one can see, Brooks uses both sonnet forms in different ways. One could say she bends and molds the sonnet forms to make her own. eNotes states:
The rhyme scheme of the poem reflects the influence of the Shakespearean sonnet—three quatrains, abba, abba, cddc, followed by a rhyming couplet, ee. However, in the development of thought, it follows the Petrarchan model of structuring the poem in an octave—an eight line stanza—followed by a sestet—a six-line stanza. The first eight lines, after the initial imperatives, picture the lives of artists, and the next six lines advocate fighting the war against discrimination or tyranny in order to create an environment safe enough for nurturing art.
The poem needs the rhyming at the end for effect, so it is necessary. Without it, the same effect wouldn't be achieved.