Recognition and Gratitude
The speaker's anger in this work comes from his feeling that two great and selfless men—identifiable in context as Charles Stewart Parnell and Hugh Lane—have been denied the recognition they deserve. Two additional factors transform this into a grave injustice, from the speaker's perspective. Firstly, they have faced ingratitude from the very people they set out to help. Parnell aimed to liberate Ireland through nationalist politics, while Lane worked to bring a gallery to Dublin. By setting the poem in Dublin and referring to it as a "town" rather than a city, Yeats emphasizes the intimate, communal nature of the betrayal these men have faced. Secondly, Yeats suggests, Parnell and Lane have not merely been ignored. In fact, the poem mentions a monument to Parnell, making clear that he is recognized in some capacity. However, this recognition is outweighed by the sheer weight of hostility and insult Parnell and Lane have faced. Indeed, Yeats hints, the amount of ingratitude and blowback a person endures is somewhat proportional to the gratitude they truly deserve.
Death
This poem presents two views of death, which are somewhat in tension with one another. On the one hand, death is not a respite from life's problems—Parnell remains as a ghost, and an "unquiet," dissatisfied one at that. He retains hope that Dubliners have changed, but also is vulnerable to disappointment when they do not. Even if the ghost is understood to be a symbol of Parnell's legacy, rather than a literal manifestation of the supernatural, this legacy is clearly unsettled long after Parnell has died. At the same time, Yeats presents death as a refuge to at least an extent. It allows the shade to retreat under the "Glasnevin coverlet," isolating himself from the people who have hurt him. Death is presented here as an uneasy in-between, at least for well-known figures like Parnell. It robs the shade of agency, turning him into a hopeful but helpless spectator.
Social Norms
Dubliners are characterized here as petty and conventional, more interested in adhering to social norms than in improving their own lives and the lives of their children. Yeats depicts Hugh Lane and Charles Parnell as representatives of two lofty, worthwhile goals: bringing art to the people of Dublin, and bringing political sovereignty to Ireland. Rather than welcoming these forces for good, various enemies of these men have worked to dismantle them. Worse yet, according to Yeats, Dubliners as a whole have not so much rejected Parnell and Lane's ideas as they have joined a mob set on renouncing them. In other words, they have turned on Parnell and Lane because social norms dictate that they should. The specifics of Parnell's downfall in real life add another dimension to this critique. Parnell was a major political player brought to disgrace after committing adultery. Thus, Yeats suggests, Parnell's violation of a social norm was unjustifiably seen as more important than his work on behalf of Ireland's people.