Trifles sets forth the subtext that women in society are marginalized, ignored, and treated poorly compared to men. The big reveal in the end of the play shows that Minnie has murdered her husband because of how badly he treated her, and yet the male investigators don't even consider spousal abuse from the husband's side. They assume that there was hysteria or a mental issue and ignore the evidence -- which is seen and interpreted by the women -- that Minnie was unhappy.
COUNTY ATTORNEY: [Looking around.] I guess we'll go upstairs first -- and then out to the barn and around there. [To the SHERIFF.] You're convinced that there was nothing important here -- nothing that would point to any motive.
SHERIFF: Nothing here but kitchen things.
(Glaspell, Trifles, etext.virginia.edu)
The story also shows that women don't have much recourse to improve their stations in life because their concerns are ignored. Without someone to see the abuse and take steps, Minnie was driven more and more to helpless anger. The two other women lament that they didn't visit more often, which could have allowed them to see the problems and help. The men expect the women to be worried only about "trifles," or matters of no consequence; in reality, the women discover the truth while the men remain oblivious.