Paul F. Cummins, Richard Wilbur : a critical essay, Eerdmans, 1971.
The poem compares the life and work of St. Paul with the caddis fly, and the poem’s fisrt person narrator sees this analogy as reflecting the fundamental dilemma of human experience.
The dual world of Paul and the caddis flies than helps the narrator to clarify his own predicament.
Now he saks « What stays ? » What is of lasting value ? Only those who follow the example of Paul and the caddis fly wil learn the answer : only those who reject simplistic and rigid.