This Is Water is David Foster Wallace's commencement address to the 2005 graduates of Kenyon College.
It's also the closest DFW ever got to writing his thoughts on the "meaning of life". It doesn't take long and you may or may not agree with any of it, but he was an brilliant writer with a genuine desire to understand things and that makes it valuable as a record of his thoughts on the matter.
You can find the whole speech on youtube or online elsewhere instead of buying the book, which is stretched to reach "book length."