Background:
Jesus told the parable of the Good Samaritan in response to the question by a Lawyer "Teacher, what shall I do to inherit eternal life?"
Jesus answers, "What is written in the Law? How does it read to you?"
The Lawyer replies, "You shall love the LORD your God with all your heart, and with all your soul, and with all your strength, and with all your mind; and your neighbor as yourself."
[Love your neighbor is part of the law from Leviticus 19:18
Jesus says "You have answered correctly; Do this and you will live."
The lawyer then asks "And who is my neighbor?"
Jesus responds with the parable.

The Story: Luke 10:25-37
A man was going down from Jerusalem to Jericho; and he fell among robbers, and they stripped him and beat him, and went off leaving him half dead.
A priest was going down on that road, and when he saw him, he passed by on the other side.
And likewise a Levite also, when he came to the place and saw him, passed by on the other side.
A Samaritan came upon him; and when he saw him and bandaged up his wounds, pouring oil and wine on them; and brought him to an inn, and took care of him.
On the next day he took out two denarii and gave them to the innkeeper and said, 'Take care of him; and whatever more you spend, when I return, I will repay you.'

Some Points:

• The Samaritans were a mixed race between the Jews of captivity and the Samaritan people of the land they were captive in. The relationship between the Jews and Samaritans was one of hostility because of some bad things that happened in the past.
• If the person lying there is a non Jew the priest could be risking defilement (becoming unclean), especially if the person were actually dead.
• Jesus was like the Samaritan. He was willing to touch the unclean. He was willing to go to the lost, the outcast, and the needy. And, like the Samaritan, Jesus was an outcast in the eyes of the Lawyers, Priests, Scribes, Pharisees, and Saducees.
• The robbers hurt the man by violence, the Priest and Levite, by neglect. All three are guilty. "To the one who knows the right thing to do and does not do it, to him it is sin," (James 4:17).

Links:
How to Explain the Good Samaritan Parable | eHow.com
The Good Samaritan Luke 10:25-37 | Christian Apologetics and Research Ministry