In this quote, Reverend Hale uses a Biblical allusion as both a warning and explanation for John Proctor. Taken from Act III of The Crucible, Hale still believes that the town and the girls are afflicted by an unseen unnatural force. While Proctor is, understandable, distressed that his wife has not only been accused, but is being arrested along with Rebecca Nurse and Martha Corey.
As these women, some of the most well-known and righteous people in Salem are being arrested, Proctor implores Hale about Rebecca "How may such a woman murder children?"
Hale's response alludes to the bible story's about the devil which state that at one time he was a favored of God and lived in heaven with him. He was not banished to hell until he went against God and thus "fell from Heaven. Hale is suggesting that these good women may have fallen in a similar manner.