I’ve run into this a couple of times in the past few weeks and think it needs addressed: that the term “neighbor” in the Bible is a negative term used to describe people of similar beliefs, that Christians don’t know what it means to “love your neighbor as yourself.” I happen to disagree with this assessment based on the Parable of the Good Samaritan. I’ve said it before and I’ll say it again, in this parable, we clearly see who are neighbor is.
The lawyer’s question (Luke 10:25-28) is paralleled in Matthew 22:34-40 and Mark 12:28-34. The parable itself is unique to Luke in the Synoptic tradition.
Just then a lawyer stood up to test Jesus. “Teacher,” he said, “what must I do to inherit eternal life?” He said to him, “What is written in the law? What do you read there?” He answered, “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.” And he said to him, “You have given the right answer; do this, and you will live.”
But wanting to justify himself, he asked Jesus, “And who is my neighbor?” Jesus replied, “A man was going down from Jerusalem to Jericho, and fell into the hands of robbers, who stripped him, beat him, and went away, leaving him half dead. Now by chance a priest was going down that road; and when he saw him, he passed by on the other side. So likewise a Levite, when he came to the place and saw him, passed by on the other side. But a Samaritan while traveling came near him; and when he saw him, he was moved with pity. He went to him and bandaged his wounds, having poured oil and wine on them. Then he put him on his own animal, brought him to an inn, and took care of him. The next day he took out two denarii, gave them to the innkeeper, and said, ‘Take care of him; and when I come back, I will repay you whatever more you spend.’ Which of these three, do you think, was a neighbor to the man who fell into the hands of the robbers?” He said, “The one who showed him mercy.” Jesus said to him, “Go and do likewise.” (NRSV)
The Greek word πλησιον meaning neighbor (from πελας)  appears 17 times in the New Testament and 4 times in Luke.
The response of the lawyer, “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.” is a combination of two Old Testament verses: Deuteronomy 6:5 (The Shema) and Leviticus 19:18b. In Matthew and Mark, these two commandments are kept separate. The combining of the two commands is a Lukan redaction.
It is important to know who the Samaritans were. The Samaritans were a group of Jew that broke away from the orthodox Jews sometime around the 6th century BCE. They had their own temple on Mt. Gerizim. The Samaritans worshiped the same God as the Jews and much of their rituals were similar to the Jews.
I’m not going to sugar coat anything. In the context of 1st century Judaism, the Jews and Samaritans did not like each other, and that is putting it mildly. In fact, these two groups were quite hostile towards each other and it’s pretty safe to say these two groups hated each other. For the Jews, Samaritans fell somewhere around women and dogs, which is pretty low on the social pecking order scale. They were viewed as half-breeds because they would marry non-Jews.
We also have to keep in mind the account in Luke 9:52-53.
And he sent messengers ahead of him. On their way they entered a village of the Samaritans to make ready for him; but they did not receive him, because his face was set toward Jerusalem. (NRSV)
With these in mind, it is quite surprising that the hero of the parable is, in fact, a Samaritan. By doing this “Jesus challenged the longstanding enmity between Jews and Samaritans.”  The boundaries of social position – race, religion, or social position – are shattered as the Samaritan and not the priest or the Levite stop to help the man left for dead.
The question, “Who is my neighbor?” was an important question for the early church. For this we can turn to Leviticus 19:17-18:
You shall not hate in your heart anyone of your kin; you shall reprove your neighbor, or you will incur guilt yourself. You shall not take vengeance or bear a grudge against any of your people, but you shall love your neighbor as yourself: I am the Lord. (NRSV)
On the surface, Leviticus 19:18 appears to be talking about members of the community. However, this section of Leviticus needs to be read as a whole and it also includes Leviticus 19:33:
When an alien resides with you in your land, you shall not oppress the alien. The alien who resides with you shall be to you as the citizen among you; you shall love the alien as yourself, for you were aliens in the land of Egypt: I am the Lord your God. (NRSV)
Like Jesus often does in parables, longstanding concepts and divisions are challenged. As R. Alan Culpepper notes,
Jesus’ parable, therefore, shatters the stereotypes of social boundaries and class division and renders void any system of religious quid pro quo. Neighbors do not recognize social class. 
I recently read an article by Graham Pockett entitled “Who is my Neighbor?” In the article, Pockett retells the parable for a modern audience. He also states that the parable:
[S]hould have been called the “The Parable of the Good Acts of a Samaritan” because He was talking about how we should behave towards our neighbors (our acts of faith – James 2:14-26) rather that how righteous we are (or should be). 
Christ came “not to abolish the law or the prophets” but to “fulfill them.” (Matthew 5:17) and simplified, the law is “Love of God and love of neighbor.” (Luke:10:27) As seen in the parable, our neighbor is not just limited to those who have similar beliefs. This is supported in the Christian tradition by Jerome:
Some think that their neighbor is their brother, family, relative or their kinsman. Our Lord teaches who our neighbor is in the Gospel parable of a certain man going down from Jerusalem to Jericho….Everyone is our neighbor, and we should not harm anyone. If, on the contrary, we understand our fellow human beings to be only our brother and relatives, is it then permissible to do evil to strangers? God forbid such a belief! We are neighbors, all people to all people, for we have one Father. Homily on Psalm 14 (15). 
Our neighbors are everyone around us; from our immediate community to the world community.
 BDAG, 794.
 R. Alan Culpepper, “Luke” in The New Interpreter’s Bible Commentary, Volume IX, (Nashville: Abingdon Press, 1995), 229.
 Ibid., 230.
 Arthur A. Just Jr, ed., Ancient Christian Commentary on Scripture, New Testament III: Luke, (Downers Grove: InterVarsity Press, 2003), 179.