The central theme of the poem "To Marguerite" by Matthew Arnold is human isolation. This is one of a group of poems, of which the best known is "Dover Beach", written by Matthew Arnold in response to a failed romantic relationship with a young French woman, He sees the isolation of England as an island, and the Dover straits separating England from France, as metaphors for his feelings about being separated from Marguerite:
Yes: in the sea of life enisled,
With echoing straits between us thrown.
Dotting the shoreless watery wild,
We mortal millions live alone.
In this poem, Arnold struggles with a loss of faith as well, because individual isolation would not be complete if "the sea of faith" had not retreated. Where for his father's generation, the personal situation of separation from a beloved would be balanced by a constant sense of the presence of God, Arnold himself no longer has that reassuring personal religious certainty.
In "To Marguerite," Arnold writes of estrangement and loneliness, imagining that the gulf that separates each of us from others to be like a sea. In contrast to Donne's contention that "no man is island," Arnold envisions us all as little islands. We long for deep communion with others, but we are cut off. Arnold envisions humankind as once a single continent and writes that we have a "longing like despair" (he uses the word "longing" twice in the poem) that once again our "marges" or edges might meet.
In saying we were once one continent, once a true community of people who were not isolated and estranged, Arnold looks back to a better time, implying that the isolated way we now live is not how life necessarily has to be. As he looks around, trying to understand what caused the current separateness, he fixes on God as the answer:
Who renders vain their deep desire?—
A God, a God, their severance ruled.
Arnold leaves it an open question which God—he says "a" God, not "God"—caused this or why this God rules for separation, perhaps suggesting the situation could change. He leaves the reader with a lonely final image: that of us cut off by the "salt, estranging sea."