Luke tells us the motive himself: the lawyer was "willing to justify himself" (Luke 10:29). Barnes explains that he was "desirous to appear blameless, or to vindicate himself," and to show that he had kept the law, though he adds that perhaps the man wanted to justify asking the question at all. If "neighbour" could be defined narrowly, he could claim he had done what it required. Gill says that by neighbour he meant only an Israelite, one of the same nation and religion, and that this is how the Jews commonly took the word. Matthew Henry observes, "Many ask good questions with a design rather to justify themselves than to inform themselves."

Jesus did not give a definition. He told a story (Luke 10:30-35). A man going "down from Jerusalem to Jericho" was robbed, stripped, wounded, and left "half dead." A priest and then a Levite saw him and "passed by on the other side." A Samaritan "had compassion on him," bound his wounds, brought him to an inn, and paid for his care. Then Jesus turned the question around: "Which now of these three, thinkest thou, was neighbour unto him that fell among the thieves?" (Luke 10:36).

The lawyer was quoting Leviticus 19:18, which commands love for "the children of thy people." The same chapter also commands Israel to love the stranger who lives among them "as thyself" (Leviticus 19:34). Barnes says the Pharisees held that only Jews were to be regarded as neighbours, and that the duty did not extend to Gentiles.

The Greek word for neighbour, plesion, simply means "near." Thayer's lexicon notes that in Jewish use it meant a fellow member of the Hebrew nation, but that in Christ's teaching it means any person, irrespective of race or religion, "whom we chance to meet," a sense Thayer says is "clearly brought out in the parable Luke 10:25-37."

The lawyer wanted to know where his duty ended. Jesus answered by showing what love looks like when it doesn't ask that question. The hero of the story is a Samaritan, a man the lawyer, by the common Jewish reading Gill describes, would not have counted as his neighbour.

Thayer points out that the lawyer used "neighbour" for the person who is owed love (Luke 10:29), while Jesus' closing question uses it for the person who shows love (Luke 10:36). Barnes says every sinner wants to justify himself, and will twist the meaning of the law rather than shape his life by what it requires. Jesus refused to let the law be made smaller. Instead He made the lawyer look at mercy itself.