What does Elizabeth want John to do? Why does he hesitate?

Elizabeth wants her husband to go into Salem and tell Ezekiel Cheever what Abigail told him during their accidental meeting the week before. Elizabeth wants her husband to expose Abigail's lie— specifically that Abigail admitted that witchcraft had nothing to do with Betty's illness. John hesitates because he doesn't want the townspeople to suspect or learn about his previous affair with Abigail.