Compare Pip's initial reaction to Magwitch (ch 39) to Pip's concern for his safety (ch 45) and explain the significance of this change.

Dickens divided his novel "Great Expectations" into three parts for specific reasons, one of which was to reveal the stages of Pip's growth.  As a dynamic character, Pip moves from his innocence and unconditional love of Joe and kindness to the convict in Stage 1 to a value system based upon social status in Stage 2 of the novel.  For instance, he becomes ashamed of Joe because he does not possess the social graces of such gentlemen as Herbert and feels that Miss Havisham's social status makes her  a superior benefactor--even though she is insane--over a lowly criminal such as Magwitch. 

Now, in Stage 3 the reader perceives that Pip has grown in his thinking.  For, he has come to understand what Mr. Jaggers has told him earlier in the novel:  "Take nothing on appearances." That is, social status is merely a mask for what a person is.  The truly good people, the people with real human values, are the "common" ones: Joe, Biddy, Magwitch.  In Chapter 45 Pip sees what kind of a person Magwitch is, not what he appears to be as in Chapter 39 of Stage 2 in which Pip has held false values. 

There is a quote from Carl Jung which explains the transformation of Pip:

Your vision will become clear only when you can look into your own heart.  Who looks outside, dreams; who looks inside, awakes.