Death
This poem is consumed with the concept of death. Multiple references are made which can be interpreted as symbolizing the unknown abyss. The reference to "all humbling darkness" in the third line is one the more easily accessible symbols of death. This is death in the abstract as a part of the life cycle of every living thing with the inclusion of "all" to signify its shared universality.
Chaos
The image of the silence of "zero hour" is described as a "sea tumbling in harness." This sea has been harnessed, as with a wild animal that one tries to tame. The difficulty of taming a wild animal becomes impossible when applied to the sea. Water is a traditional and ancient symbol for life and the concept of trying to harness the chaos of living is revealed as pointless and impossible.
Zion and the Synagogue
The references in the second stanza to the "Zion of the water bead" and "synagogue of the ear of corn" are allusions to scriptural history found in the Bible. They are prefaced by the speaker insisting he must return to them. This link between the modern day setting of the death of the girl and ancient references mentioned in scripture transform them into symbols of the unending cyclical nature of life and death. This symbolism places the child's demise into a larger historical and spiritual context.
Long Friends
The girl is described as London's daughter who lies with the "first dead." This is a reference to all those that have died before and situates the girl's death as tragic, but inevitable. A particularly oblique reference is made to her being "robed" by "long friends." This is a symbolic description of worms eating the flesh of the body. The language makes it less ghastly.
Mother
Along with the veiled reference to worms, the final resting place of the dead girl also has her accompanied by "grains beyond age" and the "veins of her mother." These are both symbolic representations of the earth in which generations of the dead lay buried. The "mother" is not literal; it is a symbol more familiarly known as Mother Nature or Mother Earth. The girl has returned to the ancient symbolic dust from which she was created.
