I had my own particular reasons for choosing to read this book. There was a recent loss in the family and I had heard that this, along with A Grief Observed, were excellent books with which to help one find some perspective.
It is very important to remember when reading this, as with much of Lewis' apologetic work, that this is a layman's view, not a theological treatise. Lewis acknowledges this from the outset and makes reference to it at various points throughout the book. I have to admit, the start of the book was not what I was expecting at all. I thought the whole thing was purely a look at theodicy, though Lewis doesn't really get going on this until the second half of the book, when having spoken a little about 'pain' he then distinguishes between the physical triggering of nerve impulses and the more emotional aspect of anguish or despair, the latter of which is what is then meant when Lewis talks about pain.
Lewis opens with a discourse on the nature of omnipotence. I found it immensely helpful, as Lewis managed to enunciate what had previously been only half-formed thoughts in my own mind and on this section I found myself in near total agreement with him. Interestingly, Lewis doesn't quite pose the problem of pain in the wording commonly found today: “how can a good God allow suffering?” Instead, he states it as “If God were God, He would wish to make His creatures perfectly happy, and if God were almighty He would be able to do what He wished. But the creatures are not happy. Therefore God lacks either goodness, or power, or both.”
Lewis' view is to gain an understanding of the terms used in the above statement which is more meaningful than those used in everyday language. So having looked at what it means for God to be described as omnipotent, he then goes on to examine the nature of 'goodness' before he discusses human wickedness and the Fall, with their respective roles in pain.
At all times, Lewis gives a 'tight' argument; that is, it is not easy to summarise and every step in the train of thought must be carefully followed. So I did find myself having to go back and re-read pages on quite a few occasions. I would recommend that each chapter be read in one sitting, as it is difficult to pick up the trail if you stop mid-way, though each chapter is self-contained and gives plenty of food for thought.
Lewis ends the book with a look at hell, pain in animals and heaven. At no point does Lewis give a concise one-liner as the answer to the problem of pain. To do so would be pithy and fail to do justice to the weight of the problem. Rather, the whole book is his answer. There were some aspects which I found quite enlightening, though I did not agree with it entirely, particularly his chapter on heaven.
From a personal perspective, it did seem a little cold. While I understand The Problem of Pain was written before his wife died, with A Grief Observed written shortly afterwards, there was little I could find here that was of help at a time of need. So I think this is better read at a time when you are not facing personal tragedy, but probably beforehand.