Marriage is important.
In the world today, we see war and strife, hatred, marital breakdown. The cause, as asserted by the author, is that God has given different mindsets to Christians than to other people. He does not define Christianity in the same way as other people. He defines it as the mindset given by God to a person. Hence, some "Hindus" are really Christian, and some Christians who pray to Jesus and so forth are really Hindu.
There is a reason why God gave Christianity to the world. If you wish to marry a Christian, or a non-Christian, you would be well advised to understand what are these characteristics of a Christian person and a non-Christian person that God has given.
As a small boy or girl, you learn many things from your mother. Fathers are often out working. You learn, behaviors from your mother. And then you get married and you introduce into your marriage, things that you have learned from your parents and also you apply the rules of the game that you were given by God.
If you look around you, you will see that Christian marriages, however nice the fairy tale and however nice it seems as if they were twenty years ago, are getting worse and worse. When you reflect on history you will notice that history was not that good. War and famine followed by more war and famine. And the reason for it not being so good was because of wrong marriage. With marriages becoming worse, history will become worse.
You may say, look at America. Is this not a success? The North American Indians are gone. They cannot answer you. But, they may have a last word on this subject. The way marriages operate in the world today, the North American Indians will answer you.
It is for this reason that the author suggests that you need to read this book. To understand the people around you and their points of view. What they want to do and what they will do. Do you want your life to be a battlefield in the future or do you not?