Desiring to justify himself (θελων δικαιωσα εαυτον). The lawyer saw at once that he had convicted himself of asking a question that he already knew. In his embarrassment he asks another question to show that he did have some point at first:

And who is my neighbour? (κα τις εστιν μου πλησιον;). The Jews split hairs over this question and excluded from "neighbour" Gentiles and especially Samaritans. So here was his loop-hole. A neighbour is a nigh dweller to one, but the Jews made racial exceptions as many, alas, do today. The word πλησιον here is an adverb (neuter of the adjective πλησιος) meaning ο πλησιον ων (the one who is near), but ων was usually not expressed and the adverb is here used as if a substantive.