The message of the poem "Limbo," by Seamus Heaney, is to directly criticize the Roman Catholic Church in its belief of saving human souls through baptism, and in its almost oppressive control over Northern Ireland. In Catholicism, limbo is a place afterlife where the souls of those not saved reside because they can't reach heaven, but don't deserve hell, so "Limbo" as it's titled immediately implies a religious allusion or focus within the poem. As the poem moves on, the focus shifts from the mother and her infant more to the religion as well. The variety in the sentence length serves to create tension in the poem, relating to the pain the mother feels from losing her illegitimate child due to the strict social pressures of Catholicism. .
Heaney reveals the setting and situation of the poem in the first stanza. First, he mentions Ballyshannon, a small river town in Northern Ireland, which provides historical context for the type of society and lifestyle of that town. With the second and third line, it is revealed that the fishermen have "Netted an infant last night/Along with the salmon" (2-3). There is a religious allusion as fish is a well-known symbol of Christianity, and by using the word "Along", it is implied that the infant and religion are somehow connected. The infant is also framed to be less of a human being and similar or equal to the fish caught the night before because they are mentioned together with "Along". This serves to support the next sentence where the baby is described as "An illegitimate spawning,/A small one thrown back/To the waters" (4-6). Due to the religious association with the fish, it can be assumed that the "illegitimate" aspect of the infant is prescribed by Catholicism, implying a child born without married parents. There is also a use of enjambment between "An illegitimate spawning,/A small one thrown back.