"There has been a great deal of soft soap talked about God for the last hundred years."

To "soft soap" someone is to flatter him. Here Lewis uses the term to refer to loose, sentimental talk about God that has no basis in Scripture.

In C. S. Lewis: A Biography, A. N. Wilson chides the author for using such terms: "The language and idiom of the broadcasts has dated: ‘There has been a great deal of soft soap talked about God for the last hundred years. That is not what I am offering. You can cut all that out’ . . . or ‘I personally think that next to Christianity Dualism is the manliest and most sensible creed on the market’ [p. 42]. It is hard to read these sentences without a smile." (180-81)