This quote, from about two-thirds of the way through Hemingway's 1952 novel The Old Man and the Sea, is about perseverance and brute force. At this point in the story, the old man has finally caught his marlin and is dragging it on the side of his skiff. His harpoon has been compromised, as he used much of its length to serve as a brace with which to tow the marlin he has caught. For two days, the marlin had continued to swim, towing the old man (who was bearing the resistance of the line on his body) in his boat. On the third day, the marlin slowed, and the old man finally killed him.
Not only does the old man demonstrate remarkable resolve in killing the marlin at the cost of his own physical comfort and well-being, he also admires the marlin's resolve for swimming so long while towing the man and his skiff. The old man often addresses the marlin, praising his strength and fortitude.
By the point in the novel when the old man encounters this shark, he is already weakened from his struggle to lash the marlin. As this quote demonstrates, the old man is now tasked with protecting his kill. The old man successfully kills the shark with this well-placed blow to the shark's brain. The feat is more impressive given the man's weakness and lack of appropriate weapon. Immediately after this quote, Hemingway states that the old man "hit [the shark] without hope, but with resolution and complete malignancy" (102). Perseverance will prevail even in the absence of hope, according to Hemingway's prose; however, such unchecked perseverance can be the cause of death for both man and beast.
The sea creatures in Hemingway's novel are portrayed majestically. The shark exhibits perseverance, too, evidenced by "the noise of skin and flesh ripping on the big fish." The shark's resolve, like the marlin's, has killed it.
Throughout The Old Man and the Sea, the old man is compared symbolically to the marlin he has caught. This is accomplished by his addressing the marlin, and also by the marlin's demise in spite of its resolve. The old man, too, will be destroyed, weakened almost to death by the novel's end. Both the old man and the marlin are martyred by their struggle.