The fate of the Bundren family is determined by one man's ironic belief in his own doom, which he uses to manipulate those around him for his own eventual gain. Anse Bundren gets what he wants while borrowing, stealing, and casting off those nearest to him.
Anse Bundren is a very interesting character so there are many things you could say about him in an essay. Given the complexity and the ambiguity of the novel, any number of topics are available to you as you look at Anse and his role and significance in the book.
The quest functions as the central plot in the novel and is undertaken at Anse's insistence. Without Anse, the action of the story would be completely different. With Anse and his special brand of selfish fatalism, any suffering he feels is passed on to others and magnified.
We see this when the wagon gets caught in the flooded river and Cash breaks his leg, when the stench of Addie's body draws vultures to Peabody's house and when Darl is hauled away to the mental hospital. Anse does not directly cause all these things to happen yet it is his insistence that Addie's wish is honored (to be returned to her family) which brings about the story's action.
The central role that Anse plays is made all the more interesting for his physical passivity. He has not broken a sweat in years and does not participate in any of the work involved in moving Addie's body. He merely presides over the quest and in the end buys a new set of teeth, plucking some gain from the family's misfortune and even finding a new wife.
Any of the ideas surrounding his character might serve as a topic for an essay and also provide a lead-in or opening. Specifically focusing on the selfishness and the caginess of Anse as a contrast to the honesty, generosity and sacrifice of Darl and Cash would allow for a narrow focus yet provide enough breadth of material to make a good essay.