According to the passage, Adolf Hitler believed that holding Stalingrad was important because he thought it would cause the greatest difficulties for the USSR. It is mentioned that by breaking traffic on the Volga at that spot, the Germans would cause the Russians significant challenges. Hitler's belief that Stalingrad was a key position and holding it would create problems for the Soviets suggests that he saw it as a strategic move to weaken the enemy. The passage does not indicate that he wanted to secure the Soviet Union to help defeat the Sixth Army. Additionally, while the harsh Soviet winter is mentioned, it is not explicitly given as Hitler's reason for wanting to hold Stalingrad. Finally, although the passage mentions that Stalingrad became a symbol for Hitler, it does not elaborate on this aspect as a reason for its importance.