Dickens wants people to sympathize with Magwitch and see him as a mostly innocent victim.
From the beginning, Dickens presents Magwitch in a sympathetic light. Although the convict terrifies young Pip and threatens to kill him, it is very clear that Magwitch is cold, hungry, hurt and afraid.
When Magwitch asks Pip where his mother is and he points, Magwitch starts to run away before realizing that Pip is pointing to a tombstone. Pip tells him good night before leaving, and Magwitch wishes he were a frog or an eel. It is a peculiar thing to say to someone you are trying to make fear you. It is a moment of weakness.
At the same time, he hugged his shuddering body in both his arms—clasping himself, as if to hold himself together—and limped towards the low church wall. (ch 1, p. 6)
The reader’s first impression is of pity, not fear. Even though young Pip is afraid, he clearly pities Magwitch too. When Pip returns to give Magwitch the food, he says the marshes are a bad place to lay, and cause rheumatism. Magwitch becomes almost conversational, and thanks Pip.
When Pip says he saw another man, the one he thought was Magwitch’s accomplice, Magwitch is excited. He even forgets to pretend that the man Pip saw was the imaginary “young man” who was going to eat him.
Later, when Magwitch confesses to taking the food in order to save Pip from punishment, we see that he is actually kind-hearted. He shows this side of him when he returns to visit Pip in London, to see the gentleman he has become.
Magwitch made his fortune in Australia, but he sent it home to Pip. He wanted to show his appreciation, and he thought Pip was a good person for helping him. He also wanted to show that anyone could become a gentleman, because the jury blamed him and not Compeyson at his trial. Compeyson looked and spoke like the upper classes, and Magwitch did not.
Thematically, there are several elements connected to Magwitch. First of all, there is the concept of class distinction. Magwitch is clearly a member of the lower class, but that does not make him less of a good person. He demonstrates compassion. He also shows the importance of love in all of its forms, because Magwitch loves Pip as a son. Through his relationship with Magwitch at the end, before Magwitch dies, Pip becomes a better person.