Whoever destroys a soul, it is considered as if he destroyed an entire world. And whoever saves a life, it is considered as if he saved an entire world.
At the first Seder I attended, the grandmother of the host had been found as a survivor of Auschwitz by her son; she had been so traumatized that she had not spoken since he had found her, late in 1946. I have always loved the song Dayenu, and that night, before we sang it as part of the Seder, I asked that we sing ALL the verses, and we did, although people usually sing only the first verse.
As we began to sing the third verse, something strange happened. Grandmother began tapping the table with her index finger, keeping time. By the fifth verse, she was singing along! We sang it to the end, and she sang with us. As we finished, she spoke, and said,"My family! We sing this."
I felt as though we had led this soul out of the darkness of evil into the Light of the Messiah. I believe we did, because she began talking afterward.
This is a true story and I am blessed to have witnessed it.