Samaritans were the descendants of those Hebrews who intermarried with pagan peoples as the result of Assyria's capture of the northern kingdom of Israel in 722 BC. They were not looked upon favorably by first-century Jews. In fact, the Jews hated the Samaritans and the Samaritans hated the Jews, so Jesus' use of a Samaritan as the example of a good neighbor in today's passage would have been striking to His original audience.
Christ told the parable of the good Samaritan in response to a lawyer who wanted to know how to inherit eternal life (Luke 10:25). Jesus' initial response was to tell the lawyer that all he had to do to live forever was to love God with all his heart and to love his neighbor as himself (vv. 26–28). We should note that Jesus was not endorsing the view that we can make ourselves righteous before God by our obedience. After all, He taught on other occasions that only those who cast themselves wholly on the Lord's mercy are justified, or declared righteous in the sight of our Creator (18:13–14). Instead, Jesus' proposal of keeping the law's two great commandments was in keeping with a strategy He employed at other times, namely, to get people to consider just how completely they had actually kept the law. His in-depth explanation of the law in places such as the Sermon on the Mount (Matt. 5:21–48) as well as His words to the rich young ruler (Mark 10:17–22) were spoken to get people to see that their estimation of their obedience was far greater than the reality, and that they would have to give up relying on their obedience for their justification.
In the course of our Savior's conversation with the lawyer about loving God and neighbor, Jesus told the story of the good Samaritan in order to illustrate who our neighbors are and how we should treat them (Luke 10:29–37). A Samaritan would never have been expected to help a Jew, but the other Jews mentioned—a priest and Levite—should have cared for the fallen man. In a day when one's neighbor was defined by blood, the failure of the priest and Levite would have been particularly scandalous. But the Samaritan's care for the injured Jew shows that we are not to limit the definition of neighbor only to those who are like us. We are not to pass by when we see someone in need and we can do something to give them true assistance. The kind of love God commands us to show is not limited by bloodlines.
Dr. R.C. Sproul points out that the Bible never talks about a universal brotherhood of man. Only those who trust in Jesus alone for salvation are God's beloved children, so a non-Christian cannot, theologically speaking, be our brother. But the Bible does talk about the universal neighborhood of man. All men and women are our neighbors regardless of whether they are Christians. And we are to love them all.