The sad thing—well, one of the sad things—about Pendleton is that Birdy (and therefore, us) learns very little about him before he dies. We know he's from Leetown, West Virginia, that he has two daughters, and that his drawl thickens as the war goes on. But he's pretty quiet, and Birdy doesn't try to get to know him.
Birdy isn't the only one. At Pendleton's memorial, no one has anything to say about him.
So why is he even in the story? To show how guilty Birdy feels about not getting to know him.
Why didn't I know more about him? […] Why didn't I sit with him and talk to him and try to understand what made him who he was? (12.202)
Pendleton's death reminds Birdy not to write people off. When he finds out another soldier in his squad has kids, he purposely asks to see their photos, because he hadn't looked at Pendleton's photos of his kids. He doesn't want to take another soldier for granted.