Although not strictly a formalist, Moore arranged her poems in intricate patterns with a poetic craftsmanship of the highest order. Why did she keep rewriting her poems? Because she was never satisfied. A meticulous, even fastidious poet, she agonized over each piece, not only while she was writing it but for decades afterwards.
Consider the construction of “Poetry,” the poem of the day, and then consider all the labor that went into it:
The poem consists of five stanzas, four with six lines and one with five lines (the third). Why does one stanza have one line fewer than the other stanzas? I'm not sure, but I suspect this discrepancy never ceased to torment her.
As far as I can tell, the first line of each stanza consists of 19 syllables. The second line has 21 or 22 syllables; the third line either 11 or 12; the fourth line five or eight; the fifth line also five or eight; and the sixth line 13 or 14.
So we can see that, within the rules she made, she allowed herself a little freedom, or at least the illusion of freedom. But in addition to being a master of syllabic verse, Moore was a consummate rhymer. In fact, there is a tension between the rhymes and the syllable count, as if she had to compromise one in order to accommodate the other. This would explain the discrepancies, as well as the compulsive need to revise.
At any rate, the rhymes in “Poetry” come in several varieties, including end rhymes (in/genuine, eyes/rise, hand/and, of/above, we/be/poetry), slant rhymes (fiddle/unintelligilbe, what/bat/not) and internal rhymes (all/ball, place/base, I/high, tree/flea/triviality). And this is but a partial count.
In the battle between expedience and ecstasy, let us hope that Marianne Moore always had a surplus of the latter.