I think this is one of the most bizarre things I have heard in a sermon. In the first five minutes, the audience completely misses the gravity of what John Piper is saying and laughs at almost every line. Even when Piper seeks to call them back, they still laugh!
This link, and the comments, express pretty well what happens when an audience expects a sermon to be loaded with entertaining elements and so interprets serious statements as humour.
Sit back, listen, and feel the sense of disbelief…
(HT: Miscellanies)
Doggie's Breakfast 
How strange!
I could see why people laughed at some of the stuff at the beginning, but it gets more and more bizarre.
I remember being very impressed with reading the script, when it first came out [about a month ago?]…
I’ll listen to it tonight.
It gets more and more weird as it goes on, and is almost impossible to listen to.