Answer:
"John Proctor reminds Mary a few times of this quote from the book of Tobit (also known as Tobias). This book is part of the Biblical Apocrypha, which some Christians consider to be part of the biblical canon. In this Apocryphal story, Tobias sends his son, Tobiah, on an errand. Tobiah goes, unknowingly, with an archangel (who is disguised so he cannot recognize him). According to this story, Tobiah meets a woman named Sarah who was plagued by a demon. This demon keeps killing her husbands on their wedding nights, which leaves her in great despair. Tobiah grows to care about Sarah and decides to marry her, despite the demon. Raphael tells Tobiah that no trouble will come to him if his behavior is good. In other words, because his love for Sarah is good, the demon will not overpower them. Raphael also gives him instructions to use a special fish's heart and liver to ward of the demon on their wedding night. On the evening of their marriage, Tobias is able to drive off the demon by faithfully following Raphael's instructions.
In this scene in The Crucible, John Proctor is encouraging Mary to tell the court the truth about Elizabeth and the doll that Mary gave her. Previously, Elizabeth was accused of being a witch because she owned a doll that had a pin stuck in its belly. Mary made this doll as a gift for Elizabeth and put the needle in the stomach to store the needle. Abigail, who saw this, used the opportunity to try to get Elizabeth in trouble. Abby stuck a pin in her own stomach and accused Elizabeth of using the doll to put a curse on her.
John Proctor knows that Mary is afraid to oppose Abigail by telling the court the truth. Abigail has gained such a powerful position in the Salem Witchcraft Trials; the judges listen to her accusations closely. John Proctor reminds Mary that there are Biblical examples where people do hard things for the right reasons and evil is conquered. Unfortunately, Mary eventually gives up; she abandons John and Elizabeth Proctor and allies herself with Abigail and her lies. She chooses to keep herself safe rather than to do the right thing."
