From the post:
Lovecraft wrote at a time that the world was moving through monumental industrial and geopolitical changes. Science was coming to terms with the theories of evolution, the discoveries of distant galaxies, and the idea that the universe was far older than anyone had previously thought. Humanity's place in the universe was rapidly shrinking.
Lovecraft's eyes were opened to the idea of an unknown universe. The idea that humans were central or important to existence was almost laughably fragile—constructed by humans as a screen meant to preserve their own sense of self-worth in the face of a cruel or unfeeling cosmos. And what if we weren't the only intelligent entities? What if there were others?
The fear of the unknown pervades Lovecraft's fiction, its infused in the larger Mythos, and it runs pell-mell through the Arkham Horror Files universe. But where the characters in most Lovecraftian stories typically respond to their discoveries with a growing sense of futility, the characters in the Arkham Horror Files universe experience a growing sense of need. They must fight, race, explore, and do whatever it takes to defend humanity's continued existence, even if there are no permanent solutions.
This is why the Arkham Horror Files setting book is presented as a collection of short stories: the way that its heroic investigators rise to meet the challenges before them represents the single most important divergence between the Arkham Horror Files setting and the Lovecraftian Mythos.