This narrative poem starts out very close to the subject, the opossum, in a distant manner. The physical description is on point as the setting of after hours bar scene and the reactions. Then in some point in the poem, there's a literary expanse that redirects the poems point of view -- as though the speaker wants this to mean more. By wanting this moment to mean more, the speaker then projects what everyone else's wants.
But first, where are we? "At Wilshire & Santa Monica" -- I haven't been there personally, but it's probably somewhere in L.A. -- does that mean that this poem is dependent on place? No and Yes. The poem does go universal in some places, but I feel this poem is specifically talking about what it's like in LA -- the "opossum / Trying to cross the street" becoming more of a symbol based on reaction.
And this is what the opossum is trying to do:
[...] It was late, the street
Was brightly lit, the opossum would take
A few steps forward, then back away from the breath
Of moving traffic. [...]
There is literally a road dilemma here -- the opossum, for some unknown reason, wants to cross the street and is aware of the surroundings. Just as the bar patrons are aware "would approach as if to help it somehow." The simile here is important here for two reasons: 1) The simile implies the actions of the people rather than stating their purpose 2) This shows a separation between the people and the opossum.
The reaction the opossum gives has in depth physical detail which expands to bigger analogous concepts:
The reddened gums, the long rows of incisors,
Teeth that went all the way back beyond
The flames of Troy & Carthage, beyond sheep
Grazing rock-strewn hills, fragments of ruins
In the grass at San Vitale [...]
These lines are more of a set-up to the long "who then" lines at the end of the poem.
There was nothing to be done for it. Someone
Or other probably called the LAPD , who then
Called Animal Control, who woke a driver, who
Then dressed in mailed gloves, the kind of thing
Small knights once wore into battle, who gathered
Together his pole with a noose on the end,
A light steel net to snare it with, someone who hoped
The thing would have vanished by the time he got there.
This is a huge portion of the poem to quote, but these lines tie in together -- these are repercussion lines. Lines that respond to the threat of the opossum, remember, the oldest living thing in L.A. The responsibility is shifted from LAPD to Animal Control. And then we, as the readers, are shown what actions the person has to do, "then dressed in mailed gloves, the kind of thing /Small knights once wore into battle" humorous, yes, but note how the actions keep referring to the past. And instead of big battles like the burning of Troy or San Vitale -- this refers to an opossum which represents the oldest living this in L.A. -- something that wants to do things a certain way versus someone who is obligated to do something a certain way.
This is where hope comes in -- the hope that "The thing would have vanished by the time he got there." Yes, the speaker is including purpose with the actions, but the focus is the lack of conflict here -- just the preparation, just to have things be done separately but acknowledged.