How do Proctor, Francis and Giles plan to use Mary Warren's testimony to prove that "heaven is not speaking through the children"?
All the events in The Crucible hinge on the testimony of this group of girls--girls we know are play-acting before the court in order to spare themselves punishment as well as take revenge on members of the town (and especially Elizabeth Proctor). They know the truth, as do John Proctor, Francis Nurse, Giles Corey, and even, probably, Rev. Parris. The court proceedings and the calling-out have gone too far when Elizabeth, Rebecca Nurse, and Martha Corey have been arrested. It's the final straw for John, and he presses his serving girl Mary Warren to admit they've all been play-acting before the court. Their ringleader, of course, is Abigail Williams. The three husbands intend to use Mary Warren's admission to convince the court that the girls have been putting on a show more than calling out any real acts of witchcraft. If she admits to her own wrongdoing, the hope is that the court will believe her and know the rest of the girls have been doing the same.
To her credit, and despite some faltering, Mary tries to make things right. It doesn't work, of course, as the drama continues and is now directed at her. Rev. Hale see through the charade and leaves the court and town in disgust. This is the final moment of opposition to the court until Hale appears again at the end in one last attempt to make Judge Hathorn see reason--an attempt which also ends in failure.