"nor how they sometimes fall short" (line 8) I hope this is the passage you are referring to.
This poem is regarding a cat that should go home but has soo much more to do. It expresses how the cat hears the call to come home but instead continues to enjoy its own activities.
I would say that the ideal of imagist poetry which is best reflected in this poem is that poets should be able to describe ordinary objects in new ways.
