Remember that the book is actually the result of three BBC broadcasts made during post Blitz England, a time before the invasion of Europe and when Germany (another Christian Nation) was having success almost everywhere. Surprisingly, today it is more prominent among Evangelicals than within the mainstream denominations.
As is so often the case it really needs to be seen as three totally separate subjects, a case for Christianity (IMHO the weakest of the three); Christian Behavior and Beyond Personality, and not as one single book. The initial case is based on universal morality and in fact can be applied to many different religious and secular moral systems. But after that it wanders off into unsupported assertion and in many places direct fallacies; for example, that there is no substitute source of joy than God and that people cannot yearn for something that does not exist.
It does end though with the basic mandate that to be a Christian is defined by what you do, by your behavior.
Anyone so limited that they can only spell a word one way is severely handicapped!