The significance of Magwitch bursting up suddenly from behind the graves of Pip's dead family in Chapter One should make us automatically associate him with some kind of father figure that surges up from obscurity to play a very significant role in Pip's life:

"Hold your noise!" cried a terrible voice, as a man started up from among the graves at the side of the porch. "Keep still, you little devil, or I'll cut your throat!"

The way that this unpleasant event occurs just after Pip has been dwelling upon his orphaned state and thinking about his dead parents and siblings, and then the way that Pip is set up on top of one of the gravestones whilst Magwitch interrogates him only adds to this impression of Magwitch somehow replacing Pip's dead parents, establishing parental replacements as a key theme in the novel. Consider the way for example that Pip owes his great expectations to Magwitch and Magwitch in many ways comes to be a father figure to him.