Theseus has asked what performances are available for the night's festivities. He reads and rejects each possibility until reaching the Mechanical's 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 Mechanical's sincerity and enthusiasm.