Jesus asked so that the lawyer would answer his own question. The lawyer had asked who qualified to be loved (Luke 10:29). Jesus asked instead who acted as a neighbour to the man in need. The story left only one honest answer. Gill says the lawyer "was obliged to declare" it, though the one who helped was "of another country and religion, and accounted as an enemy," because the case was too plain to deny. By asking "thinkest thou," Jesus let the man's own judgment do the teaching.

The lawyer answered, "He that shewed mercy on him" (Luke 10:37). Then Jesus gave the final word: "Go, and do thou likewise." The man who had wanted to justify himself was sent away not with a definition to debate but with a command to obey. Luke does not record what he did next.

The man "went down from Jerusalem to Jericho" (Luke 10:30). Barnes places Jericho about 15 miles from Jerusalem and describes the country between as "rocky and mountainous, and in some parts scarcely inhabited." The priest and the Levite both served God's worship; the Levites were the tribe set apart "to do the service of the tabernacle" (Numbers 3:6-7). The Samaritan was the most unlikely helper. Barnes calls the Samaritans "the most inveterate foes of the Jews," and John 4:9 says "the Jews have no dealings with the Samaritans."

The oil and wine the Samaritan poured in were, Barnes says, "often used in medicine to heal wounds." In Jesus' question, the Greek verb behind "was neighbour" is gegonenai, a perfect form of a verb meaning to become, which is why the ESV says "proved to be a neighbor." The point is not what the man was by birth but what he became by mercy.

Jesus' question reverses the lawyer's. The lawyer asked, "Who is my neighbour?" as if the answer were a category of people (Luke 10:29). Jesus asked who "was neighbour," as if the answer were an action (Luke 10:36). Thayer's lexicon notes this shift: in Luke 10:29 a neighbour is one worthy to be treated as a friend; in Luke 10:36 it is the one who performs the offices of a friend.

The story also shows how mercy crosses lines people draw. Gill, commenting on Luke 10:33, suggests that Christ "may be meant" by the Samaritan, since the Jews called Him one (John 8:48). Whether or not a reader follows Gill there, the passage itself shows the heart of God's law: love that "had compassion" (Luke 10:33) and then did something about it.