He talked about the value of practice.
"I've found that when I've done my best work as an actor it was only after I pushed myself to be better than I ever thought I could be. And I have a pretty high idea of how good I can be," he said.
"Some of you may play because you love football. Some of you may play for your grandmother. Some of you may play for your older brother, your dad. Some of you may play for the coaches. Some of you may play for the university. At the end of the day every single one of you has really only got to be playing for one person."
(He leaves it open minded, but we're guessing that one person is "you.")
Near the end of the speech McConaughey gets the team to do the humming routine from "The Wolf Of Wall Street," and then tells the players the story of how it ended up in the movie (Leonardo DiCaprio saw McConaughey warming up with the routine before the scene and asked him to do it on camera).
The players were slightly confused, but eventually joined in:
Here's the video of the speech (the humming thing comes at 3:25):