"Explanation" is a poem from Wallace Stevens's first book of poetry, Harmonium (1923). It was first published in 1917, so it is in the public domain.
This poem may be an explanation of the difference between conventional decoration and artistic imagination, the latter represented, as Buttel proposes, by an allusion to Chagall and the otherworldly charm of his paintings.
References
Explanation (poem) Wikipedia(Text) CC BY-SA