I think it is a very important chapter. In fact, I feel it is a pivotal moment in the narration about Henry, his attitude, and ability to fight. In the chapters previous to chapter 5, the reader has been with Henry during his flight from a previous battle. The reader is also walked through Henry's odd logic about how he is the smart and brave one for running away, while all of his squad mates are ignorant. Those previous chapters show Henry as a character that is entirely focused on himself.
Chapter 5, however, shows a complete turn around in attitude for Henry. A new battle begins, and unlike the first time, Henry stands and fights. He finally sees that he exists as a part of the army machine. He sees himself as something greater than an individual. He is now an important part of a well oiled machine. He fires and reloads like a madman, and is proud of his selfless efforts in the battle.
He suddenly lost concern for himself, and forgot to look at a menacing fate. He became not a man but a member. He felt that something of which he was a part—a regiment, an army, a cause, or a country—was in a crisis. He was welded into a common personality which was dominated by a single desire.