JCL is the stuff of nightmares for many programmers and operators. This book explains JCL in such a way as to have it make sense.
If you have a comfortable understanding of ordinary English and are looking for an easy way to learn JCL, this book is for you.
If you already know a little JCL and you want a handy reference guide to bail you out on commonly occurring problems with JCL, this book is for you there too.
If you're looking for an introduction to some of the advanced tricks you might have seen in MVS, this book is for you on that as well.
How can this book do all that at once? Because, contrary to its reputation, JCL is not particularly difficult; it just has esoteric aspects that make it seem difficult if you have nobody to explain things. Once explained, all seems clear.