The sentence "He was glad for one thing: the rope was off his neck. That had given them an unfair advantage; but now that it was off, he would show them. They would never get another rope around his neck. Upon that he was resolved" best illustrates the theme of resilience and determination in the passage.
In this sentence, the protagonist, Buck, experiences relief and determination after having the rope removed from his neck. This symbolizes the removal of a physical and metaphorical restraint placed upon him. Buck is determined to show those who had control over him that they will never have the opportunity to dominate him again. He resolves to resist any further attempts to subdue him.
This theme of resilience and determination is further emphasized by Buck's refusal to eat or drink for two days and nights, his accumulation of wrath, and his transformation into a raging fiend. These actions demonstrate his unwavering determination to assert his strength and independence.
Throughout the passage, Buck's actions and reactions reflect his resilience and unwavering resolve to overcome the challenges he faces. This theme of resilience and determination sets the tone for his journey in the story and establishes his character as one who will not be easily subdued.