This poem ultimately is about connection with elementary metaphysics and the sublime. It uses an orange as an example of an everyday object to demonstrate how even something as simple as an orange can act as a symbol of mercy. However, this meaning of the poem is only relevant after the bad side of humanity is fully explored.
The historical allusions in this poem refer to the mass of immigrants that ventured to America at the turn of the twentieth century. The ship, the poet's mother, and the orange, need to be seen both as symbols and as facts in this light. The ship is what is transporting the immigrants towards mercy, and the orange seems to symbolise mercy but only if the mother chooses to eat it. Symbolically, we could argue that the poem as a whole is really about the story of humans trying to come to terms with living in our universe. The way in which the poem gives a happy ending to the journey of the characters mentioned stands as a testament to the power of the human spirit and the way in which we are able to face the conditions of the world and the bad things we have done to it and yet manage to survive with hope in our hearts.