Much of this poem takes the form of an apostrophe to the speaker's dead friend, Joe. By speaking directly to someone who can't answer, the speaker suggests the almost surreal frustration and confusion of grief.
Joe remains a vivid presence in the speaker's memory. The speaker recalls how Joe used to rant and rave about "Irish kings," "English perfidy," and the "dirtier perfidy of publicans": the English might have been treacherous, Joe felt, but there was no one more treacherous than a pub owner refusing you one last drink. Joe's rowdy, funny character comes through in the speaker's memories of his "coat with buttons off" and his "gaunt chin and pricked eye," too. This was clearly an alert, intelligent man with a good sense of humor—and a person who didn't bother too much with little details like whether or not his coat buttoned shut.
With this detailed portrait in his memory, it's no wonder that the speaker feels he should be able to address Joe directly. But whenever he calls out to that long-lost "you," he's frustrated to find that there's no answer—only the persistent question of whether Joe's spirit is still out there somewhere. He even starts goading that imagined spirit into speaking louder:
Are you shouting at me, dead man, squeezing your face
In agonies of speech on speechless panes?
Cry louder, beat the windows, bawl your name!
Joe, of course, never answers. By presenting this elegy as a conversation with someone who can't reply, the poem suggests that there's something absurd about death: how, the speaker seems to wonder, can he picture everything Joe said and did so clearly, but not be able to reach him?