It is a message on sanctification that is not limited to mere exhortations on the need to have a pure heart. Much more, it is about satisfying the hunger of those who seek to know how to receive a pure heart and keep it continually pure.
In this book, Z.T. Fomum exposes the vanity of Christless religions: They distinguish their old (unclean) heart and make it look like a new (or pure) heart. The truth is that all who have an unclean heart need Jesus, regardless of their religion.
This book is like light in darkness. Read it.