This is an Italian (Petrarchan) sonnet doing a magic trick. The form requires 8 lines of setup (octave), then a turn (volta) at line 9, then 6 lines of resolution (sestet). Cullen follows the blueprint perfectly—until he doesn't.
Lines 1-12 build what looks like a conventional theodicy poem: "I don't question God's goodness, even though bad things happen." He stacks examples—moles born blind, human mortality, Tantalus and Sisyphus suffering forever. The tone is humble, even submissive: "Inscrutable His ways are," our minds are too "petty" to understand God's "awful brain." Standard 1920s religious poetry.
Then line 13 detonates everything. "Yet do I marvel"—the volta comes *late*, at line 13 instead of 9, and it reverses the entire argument. Cullen doesn't marvel at moles or Greek myths. He marvels at "this curious thing: / To make a poet black, and bid him sing!" The polite theological meditation was a setup. The real subject is American racism, and suddenly "inscrutable" reads as bitter irony.
The form itself makes the argument. Cullen uses the most European, most classical poetic structure (Italian sonnet, Greek mythology, Christian theology) to say: the cruelest paradox isn't ancient—it's being Black in America and expected to create art. The sonnet's elegance is the point. He's proving he can write "their" poetry while naming what "they" won't acknowledge.