This simile comes at a crucial point in the poem, at the very end of Part III, when Death wins all the crew except for the Mariner, who is won by Life-in-Death. The simile is used to describe the deaths of the Mariner's fellow crewmen, who, being won by Death, then die, one by one, slumping to the ground. In this stanza, the Mariner questions where their souls actually flew to:
The souls did from their bodies fly,--
They fled to bliss or woe!
And every soul, it passed me by,
Like the whizz of my crossbow!
Clearly, the simile is very appropriate because the crew in a sense are killed because of the foolish act of the Mariner in killing the albatross in the first place. Thus, in the Mariner's mind, every soul that passes him by reminds him of his act that caused their deaths in the first place: him shooting his crossbow. We are presented with a Mariner who is haunted with guilt and indeed, has been won by Life-in-Death, for his life is consumed by his deed and the consequences of his actions.