Anaphora
Anaphora is repetition that occurs at the beginning of sentences, clauses, or phrases. In this example, "a man" is repeated three times at the start of sentences. The repetition of "man" emphasizes the distinct impression this man makes on young Pip. It also foreshadows the convict's reappearance later in the novel. The fact that "man" begins the sentences is consistent with this incident being the first thing Pip remembers in his life.