A critical analysis of themes would describe and evaluate the meaning of Arnold's poem and back any ideas stated with quotes from the text. One theme in the poem includes isolation on a universal level which describes how we as humans are estranged from each other; this includes a lament that God is responsible for this situation, and the narrator's seeming sense of estrangement or distance from Marguerite.
The poem abounds in imagery of separation and isolation: we humans are on islands with "straits" (water) between us—an image that is repeated in different ways as the narrator emphasizes how humans are isolated. The narrator also plainly states, "We mortal millions live alone."
The poem also expresses the theme that we were once united. We sense this, the poet says, when we see the moonlight and the stars, feel balmy spring weather, and hear the nightingale sing. Then, we (the islands) think:
... surely once ...we wereParts of a single continent!
Critically analysing the themes of Matthew Arnold's "To Marguerite -- Continued" involves investigating the intersections of his views of religion, love, and poetry. The first theme you might consider is that of unrequited love, and in particular, how for Arnold, this seems to have some sort of cosmological and religious significance, which causes it not to be merely a portrait of the poetry of "suffering with no release in action" which he condemned in his 1853 Preface. Next, you should examine how the isolation of humans, like the division of islands by the sea, reflects the atomistic nature of our fallen condition:
A God, a God their severance rul’d!
And bade betwixt their shores to be
The unplumb’d, salt, estranging sea.