A Pointless Flame

"...Jimmy Cross crouched at the bottom of his foxhole and burned Martha's letters. Then he burned the two photographs...it was only a gesture...the letters were in his head." Page 22

I thought this passage was very interesting. I was surprised when Jimmy started burning the letters and photos. They were his only physical connection the the world outside of the war. The whole passage still confuses me a little. The gesture seemed pointless to me. He admits it was only a gesture but I don't understand the importance of the gesture. It didn't change anything which he did admit but it also didn't seem to fit the situation to me. It seemed a gesture to show rejection and disregard of the outside world not necessarily a commitment to the world of the war and his men which was his intended purpose. It was supposed to symbolize a renewed effort to protect his men and their best interests but it didn't seem to connect at all.