The Iron Heel can be seen as a challenge to the Western sense of establishment and safety that many of us are privileged to enjoy. By setting half of the plot in the past and the other half way in the future (700 years, in fact), London draws attention to the far stretches of time, and that's one of the most important features of the book.
Another aspect of the novel that needs to be addressed is the paranoia. Avis's experience of the government is ironic, since usually, in dystopian novels (1) the evil government is usually a communist dictatorship, and since (2) the evil government is usually the one in the future. In this novel, the evil government is the one from the contemporary past, and it's an oligarchy. This is essentially an indirect way of pointing the finger back at ourselves, saying that even in our present moment, the elements of tyranny are already active through the oligarchy of the wealthy and powerful.
By setting the Anthony's comments 700 years in the future, London accomplishes two things. Firstly, he makes a good argument that writing is the most sure way of leaving a legacy. It's an argument for the duration of the written word through history. Secondly, and most importantly, he reminds the reader that one day, what we regard as the present will be so far in the past that it doesn't even seem real anymore. He's making the reader focus on the transience of the present moment in the vast scope of time.
