Francis and Rebecca Nurse are two of the Puritan community members living in Salem, Massachusetts. They are also pillars of the society. Everybody considers them good Puritan people with strong, Christian values. Basically, they are the antithesis of what a witch should be.
It’s strange how I knew you, but I suppose you look as such a good soul should. We have all heard of your great charities in Beverly.
The reason that they are important to Miller's play is that they introduce doubt. They introduce doubt into Reverend Hale and the rest of the community. To Puritans, witchcraft and the threat of witchcraft was a very real thing. It wasn't fairy tale magic. It was real communion with the Devil. People began to doubt the witchcraft proceedings after Rebecca and Francis Nurse were accused, because they simply could not believe that Rebecca and Francis could possibly be witches.
Believe me, Mr. Nurse, if Rebecca Nurse be tainted, then nothing’s left to stop the whole green world from burning. Let you rest upon the justice of the court; the court will send her home, I know it.