The most forceful theme of the poem is the agony of the merman as he recounts the loss of his wife. The reader senses desperation as he urges his children to plead with Margaret to return to them: “Children’s voices should be dear/ (Call once more) to a mother’s ear;/ Children’s voices, wild with pain—/ Surely she will come again!” The merman feels that it is unnatural for her to leave her children. He is so distraught that he is even unsure of how long she has been gone: “She smiled, she went up through the surf in the bay./ Children dear, was it yesterday?” His memory of their happy times together increases the pain of his desertion, as he recalls that “Once she sate with you [the children] and me,/ On a red gold throne in the heart of the sea,” but when he pled with her, “she gave me never a look.”

Margaret has been forced to choose between the two worlds, but she has not done so without pain of her own. Although in her singing she tries to keep up her spirits, her mind wanders back to the family she has left behind as she turns from the spinning wheel and looks out to the sea: “And anon there drops a tear/ From a sorrow-clouded eye,/ And a heart sorrow-laden.”

Another theme is the Victorian loss of faith, the result of the conflict of science and religion, which had been developing rapidly through the early part of the century and was later to culminate in Charles Darwin’s On the Origin of Species by Means of Natural Selection in 1859. Although he desperately wanted to believe, Arnold felt that Christianity had simply run down as a religion, that it no longer had any vitality, a feeling that is created through the gray and white imagery. Arnold cleverly plays on the theme of faith with the merman’s song, “Here came a mortal,/ But faithless was she,” emphasizing again the fact that Margaret cannot have her conventional religion and her life with the merman as well. In going back to her former faith, she becomes unfaithful to her husband.

Margaret’s song contains images that may suggest her unconscious doubts about the validity of her religion as she sings of “the child with its toy” and then in the next line refers to “the priest, and the bell, and the holy well [the font containing holy water],” implying that in her mind those items associated with the priest are also playthings. The religion makes no attempt to be inclusive: “Loud prays the priest; shut stands the door.”

“The Forsaken Merman” is one of Arnold’s most popular and most frequently anthologized poems because of its powerful portrait of human emotion. It serves as an almost historical document of the collapse of traditional faith in the Victorian era.