Answer: Jesus, in this well-known parable, used a person from a group of despised people to illustrate that love and mercy triumphs over biases, hatred and animosity towards others. It is interesting to note, in this particular story, that Christ never uses the term "good Samaritan," although that is certainly implied (Luke 10:29 - 37).
Generally, a Samaritan would be an inhabitant of either the city or region of ancient Samaria. Over time, those who lived in this region were considered anything but good. The city of Samaria was purchased by Omri, the sixth king of Israel (885 - 874 B.C.) and named after its former owner. Over time the entire northern kingdom of Israel was also called Samaria (1Kings 13:32, Jeremiah 31:5).
After a three-year assault by Assyrian kings beginning with Shalmaneser V, Samaria fell to its enemy in 723 B.C. (2Kings 17:6, 18:9 - 12). Thousands of people were deported to Assyria while Assyrians migrated to the area. From this point onward, a Samaritan was consider "mixed" since those new in the land intermarried with the poorest Israelites that were left by the Assyrians.
The marriages between the remaining Israelites in the land and Assyrian Gentiles led to the widespread worship of pagan gods. This was the beginning of the animosity between the average person in Samaria and the Jews.
Later in history (c. 432 B.C.) a man named Manasseh, of a priestly lineage, obtained permission from Persian King Darius Nothus to build a temple on Mount Gerazim for those in Samaria because they had given him refuge (Antiquities of the Jews by Josephus, Book 11, Chapter 8, sections 2, 4). This enraged the Jews even further and solidified their belief that the people there were good for nothing.
The animosity and bitterness felt by Jews in Judea toward Samaritans cannot be underestimated. Even after a few hundred years had passed after a rival temple was built on Gerazim, they still rejected the people of the land at the time of Christ (Luke 9:53 - 54, 10:25 - 37, 17:11 - 19, John 8:48). Their hatred was so great that when they traveled from Galilee to Judea they would bypass Samaria through the barrenness of Petra just to avoid contact.
The attitude of Jews toward the average Samaritan is why Jesus used them in his parable. He wanted to underscore the teaching that we are to be merciful to all people in need, whenever we can, and not just those we like or accept. He even rebuked His disciples for being hostile toward these people (Luke 9:54 - 56).
Christ, of course, loved these people. Luke 17 gives the account of him healing a Samaritan leper and praising him for being grateful. He also honored a person from Samaria for being neighborly (Luke 10:30 - 37), asked a woman from the area for a drink (John 4:7), and preached directly to them during his ministry (John 4:40 - 42).
The meaning of the Good Samaritan parable is that we are to strive to be perfect and do good to all just like God (Matthew 5:48).