How does the author use foreshadowing in Tales of the Cthulhu Mythos?

In the tale, Beyond the Threshold, the malevolent force is Ithaqua, a wind spirit that catches victims up into the air and then transports them about the globe to random places before dropping them from some great height. The threshold of the title is heavily foreshadowed in Tony's contemplation about the great painting in the house—so heavily foreshadowed that the subsequent story becomes tiresome in the presentation of Josiah's speculation about what or where the threshold might be. In the end the result is not even supernatural—the painting merely covers a hold in the wall that leads into a cavern system through which Ithaqua—apparently incapable of supernatural ingress— travels to take Josiah away.