They asked who counts as a neighbor. He answered with who acts like one.
A lawyer asks Jesus what to do to inherit eternal life, and between them they arrive at the answer: love God, and love your neighbor. Then comes the real question — "who is my neighbor?" — asked, Luke says, because he wanted to justify himself.
The parable is the answer. And it does not answer what was asked.
Now which of these three do you think seemed to be a neighbor to him who fell among the robbers?
The man had asked "who is my neighbor?" — in other words, how far does my obligation go, and where may it stop. Jesus swaps the question. It is no longer who deserves to be treated as a neighbor, but who behaved like one. And the answer the lawyer is made to give, "he who showed mercy on him", he gives without being able to say the word "Samaritan".
Jews and Samaritans at the time avoided one another for old religious and historical reasons. A Jewish listener would expect the third character, after the priest and the Levite, to be an ordinary Jew — the hero of the people. Jesus puts there exactly the person the listener did not want to see helping.
That is why the parable resists being boiled down to "help people in need". It says that too, but the blow lands somewhere else: the question "who is my neighbor?" is looking for a boundary, and the story hands over none. It ends with a short instruction — "Go and do likewise" — addressed to someone who wanted to know where he could stop.
Walking with Jesus has a collection called The Parables of Jesus that takes them one a day — each with the question he was answering, a short reflection, a prayer, and one thing to carry into the day.
It is a one-time purchase, about five minutes a morning, and it never asks you to catch up on days you missed.