This is a very clever but also serious and reflective poem that explores the impact of the poet's presence on the surroundings where he is. The first stanza acknowledges that when he is in a field he is "the absence / of field," and as the poet goes on to explain in the second stanza, wherever the poet walks, the air always has to part, and then flood back in to fill the space which he has just occupied. This sets up the final stanza of this poem:
We all have reasons
to keep things whole.
The poet therefore believes that his presence in settings such as the field creates a sense of incompleteness, as he is in some ways disrupting the natural environment. Therefore, if he continues to keep on moving, he returns the setting that he occupies at that particular moment to its normal undisturbed self without his presence making it "the absence" of whatever it is. The final stanza is somewhat ironic, as the majority of people have very different reasons to keep on moving, but the speaker indicates that his reasons are much more philosophical.