Why does Mary warnjohn about testifying against Abigail?

Mary warns John about testifying against Abigail because she fears that Abigail will retaliate and harm them both. She understands that Abigail is manipulative and dangerous, capable of turning situations to her advantage. Mary knows that speaking out against Abigail could expose them to serious repercussions, as Abigail has already shown her willingness to go to extreme lengths to protect her own interests. Ultimately, Mary is trying to protect John and herself from the potential fallout of challenging Abigail's authority.