Lewis's shorter works were generally originally composed as speeches or as articles for periodicals. Various sets of them were collected and published in book form both during his life and after his death. Trying to determine what works are in what collections is difficult - most works appear in more than one collection, some works appear under more than one title, and some collections appear under more than one title.
To aid readers, in this review I've listed the works in this collection, with notes indicating other collections they have appeared in. Where a work has appeared under more than one title, I give both titles separated by a slash.
Table of Contents:
"Membership" (1), (2)
"Learning in War-Time" (1), (2)
"On Forgiveness" (1), (2)
"Historicism" (2), (3), (5)
"The World's Last Night" / "Christian Hope - Its Meaning for Today" (2), (4)
"Religion and Rocketry" / "Will We Lose God in Outer Space" (2), (4)
"The Efficacy of Prayer" (2), (4)
"Fern-Seed and Elephants" / "Modern Theology and Biblical Criticism" (2), (3), (5)
Notes:
(1) also published in "The Weight of Glory and Other Addresses" / "Transposition and Other Addresses"
(2) also published in "Essay Collection & Other Short Pieces"
(3) also published in "Christian Reflections"
(4) also published in "The World's Last Night and Other Essays"
(5) also published in "The Seeing Eye and Other Selected Essays from Christian Reflections"
Recommendations:
This is an unnecessary collection. It will overlap almost any other collection of Lewis' shorter writings on Christianity you might buy, and will give you no work you cannot get elsewhere. Don't buy it.
So what should you get?
If you are interested in Lewis's shorter works, my best advice is to get "Essay Collection & Other Short Pieces", which, as of the time of this writing, is available from Amazon UK but not Amazon US. That collection consists of about 130 short works by Lewis. The works in that collection are mostly, but not exclusively, Christian.
If your interest in Lewis's shorter works is restricted to those on Christianity, and your budget or enthusiasm does not run to "Essay Collection & Other Short Pieces", then my second-best advice is to get any or all of the following (they don't overlap significantly, and between them they include most of Lewis's shorter Christian writings):
"God in the Dock - Essays on Theology and Ethics"*
"The World's Last Night and Other Essays"
"Christian Reflections"
"The Weight of Glory and Other Addresses"
* Be careful - there is a UK Fontana paperback lurking about called "God in the Dock - Essays on Theology" that is substantially shorter than the "God in the Dock - Essays on Theology and Ethics" collection. A full version of "God in the Dock - Essays on Theology and Ethics" was published in the UK under the title "Undeceptions - Essays on Theology and Ethics".