How does the quote below from The Old Man and the Sea foreshadow what happens later in the novel?
well the old man is speaking to the young boy and the boy tells him that he is the greatest fisherman, quote, "there are many good fishermen and some great ones. But there is only you."
Manolin is continuing the discussion that precedes the quote, in which he and Santiago are discussing who might have been the greatest baseball manager, but is changing the topic by giving his opinion that Santiago is the greatest fisherman.
The comment foreshadows the great struggle awaiting Santiago with the "great fish." Santiago must use all the skill and tricks he has learned over the years of fishing in order to win the battle to land the marlin, demonstrating that he is, indeed, a "great" fisherman. Even more impressive, Santiago goes through the ordeal of successfully landing the marlin by himself - there was "only" him physically in the boat during the ordeal of hooking, tiring, and landing the marlin.
At the end of the story, the others in the village recognize Santiago's accomplishment. "What a fish it was," the proprietor said. "There has never been such a fish." While they do not say so directly, the others concur with Manolin's opinion that Santiago is the greatest fisherman of them all.