It is absolutely surprising that Rebecca Nurse is charged with witchcraft because, as Miller writes when he introduces her and her husband, "the general opinion of her character was so high [...]." She is widely known to be pious and humble and godly. Her mere presence is enough to quiet Betty Parris who is strangely sick in bed. She insists that if there is some problem in Salem then the townspeople should examine themselves to learn its cause; she wishes to avoid any hysteria caused by a fear of witches.
When Mr. Hale arrives, never having met Rebecca before, he recognizes her because, as he says, "I supposed you look as such a good soul should." He claims that everyone in Beverly, a town or two over, has heard of Rebecca's good works. Her reputation is so sterling that people even know her in another town and that this man of God can recognize her simply because she seems so holy. In Act Two, he insists that "if Rebecca Nurse be tainted, then nothing's left to stop the whole green world from burning." She is everything that is charitable and good, and so the idea of her being accused seems ludicrous to anyone who is likewise honest.