Why does John Proctor insist that Mary Warren go to court with him the day after Elizabeth is arrested?

John refused to wait around for the corrupt court to condemn his wife. Mary Warren made the poppet that is being used as evidence against Elizabeth. Abigail knew of this poppet and used it to act out in court. John wants Mary to confess this in court.

You're coming to the court with me, Mary. You will tell it in the court.