Neville 's one of Harry's fellow Gryffindors, and for now he seems like a fairly anonymous one. In The Sorcerer's Stone, he's simply a surprisingly klutzy student at Hogwarts: regularly bullied, terrible in fights and unable to keep track of…well, anything.
And yet he's in Gryffindor House with all of the "brave" students. Why? Well, it's probably Rowling's subtle way of saying that bravery doesn't mean having no fear. It means being terrified and doing what you need to do anyway.
Take it from Dumbledore:
DUMBLEDORE: It takes a great deal of courage to stand up to your enemies, but a great deal more to stand up to your friends.
As we learn, Longbottom has a way of fighting through his fear and doing what he has to do.Neville's on the sidelines here, but he's in Gryffindor for a reason, and it looks like he has the makings of a first-rate ally if Harry & Co will let him.