This third talk became Chapter 4 of Lewis' book 'Mere Christianity' and was originally called 'Materialism or Religion’.
You can find the book here: http://www.amazon.com/Mere-Christianity-C-S-Lewis/dp/0060652926
(12:30) "That troublesome God". See Genesis 3.24. I am referring here to the severity God showed Adam and Eve in casting them out of the garden of Eden for their sins (with no return possible to the paradise). The sin was called "treachery" by the Holy Spirit in Hosea 6:7.