Based on the lines presented, it can be understood that the speaker seems pessimistic about the relationship between human beings and their destiny and fate, and not an optimist.
When the speaker says that "Fate slew him", impersonating fate in a "She" able to take independent actions that could be uncontrollable and violent, he conveys that fate not only takes action without human's control but that those actions might be horrible. "Impaled him on her fiercest stakes", the speaker says, creating an extremely violent scene where fate tied the man in the text by impalement. The speaker keeps on describing terrible forms of violence imposed by fate upon the man, like "sapped his firm advance", where she would have tried to destroy him. Therefore, it can be understood that the speaker seems pessimistic about the relationship between human beings (here represented by the man in the story) and their fate.
