Theseus has asked what performances are available for the night's festivities. He reads and rejects each possibility until reaching the Mechanicals' offering of Pyramus and Thisbe. The description as being "merry and tragical" as well as "tedious and brief" amuses him, so he asks more about it. Philostrate explains that simple craftsman of the town have put together an absolutely absurd rendition of the play, so bad that he had to laugh at how bad it is. But he concludes with the admittance that they worked hard to put this together to entertain Theseus. This warms Theseus' heart, and he responds: "I will hear that play, for never anything can be amiss, when simpleness and duty tender it."
And it turns out that the entire court has a great time watching the play, both for the MST3K-style mocking they get to do, but also because they can see the Mechanicals' sincerity and enthusiasm.
This moment right before Act 4: Hermia is wandering alone in the woods, completely exhausted and still recovering from the terrible things Lysander said to her and the way he treated her. She's unaware that he was enchanted, and believes that he suddenly started hating her for no reason. And still, the last thing she says before falling asleep is: "Heavens shield Lysander if they mean a fray!", i.e., she's worried about him and doesn't want him to get hurt fighting Demetrius.