A - convince
because u wanna convince the reader
It's a symbol of love and sacrifice. Della really wants to give Jim a present that will go with his gold watch which was a prized possession to Jim. And Jim wanted to get Della a comb for her beautiful hair. However, they both didn't have money so they made a sacrifice to get each other a present. Della cut off her beautiful hair to get Jim the chain, and Jim got rid of his watch to buy her the comb. Even though, the gifts are now worthless it shows how they thought of each other and made a sacrifice to get each other a gift.
Although I have yet to read this novel, based on the excerpt you provided my best guess would be the uncontrollable power of nature. In my opinion, that is the only one that <span>is the interpretation of MobyDick as a symbol in the novel.
Hope this helps!!</span>