|The Good Samaritan, William Hogarth|
(from the original in St. Bartholomew's Hospital. Wellcome Images.)
Some background you may already know : The Jews and the Samaritans were enemies with a long history of estrangement, ever since the Kingdom of Israel was split in two after Solomon's death. The Samaritans worshiped God in the "wrong way," on Mt. Gerizim in Samaria instead of in Jerusalem. In the context of the Scriptural account, the full question the lawyer was asking Jesus was, "Who is my neighbor who the law says I should love as myself?" And instead of simply replying, "you should love everyone--including the Samaritans--as your neighbors," Jesus told this story in which a Samaritan loved a Jew!
After the presumably Jewish man in the story was robbed, two of his fellow countrymen and co-religionists passed him by. To touch the man, who might be dying, would have made them ceremonially unclean. The fact that one of the despised Samaritans went way out of his way and spent a lot of time and money to help an injured Jew is highly significant. Because they were enemies, anyone of that era would think that Jews and Samaritans owed nothing to each other. The Samaritan ignored the prejudices of his compatriots and helped the Jew.
So way it turned out, that the Samaritan was the good one while the two Jews who passed by were not, must have struck the Jews who were listening, and it would have been an inspiration for those followers of Jesus who might have been self-righteous about their status as the chosen people. Jesus was telling them that one of the despised Samaritans was the only one who did God's will, and it might have made them ashamed and gave them the resolution to be good themselves, like the Samaritan.
It should be an inspiration for us.
And here's another thought, there are several significant mentions in the Gospels of how Jesus seemed to go out of His way over and over during His short time of public ministry to put in a good word on behalf of those who are mistaken in how they worship God but who are pleasing to God anyway. When Jesus healed the twelve lepers, only one, the Samaritan, came back to thank Him. And Jesus shocked his disciples when they found him conversing with the Samaritan woman at the well, but through her He reached the people in her town when they saw how talking with Him had transformed her.