The boys repeatedly emphasize the importance of going to the mountain in Chapter Seven. In the previous chapter, Ralph makes a big deal about going to the mountain to relight the signal fire. Most of the hunters, including Jack, are extremely disgruntled by Ralph's forceful show of leadership, because they wanted to play at Castle Rock. Now in Chapter Seven, Jack keeps bringing up the idea of going to the mountain to search for the beast; after all, that location is where Samneric originally spotted the beast.
Jack keeps bringing up the trip to the mountain for several reasons, but mostly to annoy Ralph. He senses that Ralph is scared of the Beast, and his insistence that they continue on to the mountain is Jack's way of mocking Ralph's decision and poking at his fear.
"The mountain," said Jack, "I told you." He sneered. "Don't you want to go to the mountain?"
Jack uses his continual questioning of Ralph to undermine the other boy's authority and prove himself as the more capable leader.