What is the real reason Reverend Johnson accuses Mary of witchcraft in the novel, Witch Child?

Reverend Johnson is the haughty, cold leader of the settlement at Beulah who is hailed as a prophet. Mary dislikes his cold, empty eyes. When Reverend Johnson summons Martha to tend his sick children, he questions Mary's faith, and after his wife dies in childbirth, he asks for Rebekah's hand though she is promised to Tobias. He accuses Mary of witchcraft when his hopes of Rebekah are thwarted. Leading the witch hunt, Reverend Johnson calls for Obadiah Wilson's aid, persecuting Mary as a witch.