The fourth quote shows that the narrator is persevering through the hardships. The first quote only says that Arab Sheikh is pushing the narrator on, not that the narrator is actually trying. The second quote is quite the opposite of going on - in this one, the narrator wants to stop. The third quote only talks about the pains the narrator was experiencing, not of if he would go on or not. Only the fourth quote talks about moving on despite all the pain and aching.