What is "White Field Korean"?

This morning I received in the mail the book in the photo below. It is a 421-page Korean language textbook that was written by Bruce Grant, author of "A Guide to Korean Characters." It was published in 1982 and was written for Mormon missionaries going to Korea. The dedication in the book reads as follows:

For All Who Serve in Korea Then, Now, and in the Future 

The book has 100 lessons, and each lesson is composed of four parts. Part A is "Language Forms," Part B "Common [Chinese] Characters," Part C "Korean Proverbs," and Part D "Reading." At the end of each reading, there is also a vocabulary list labeled "Definitions."

The interesting thing about the book are the readings in each chapter. They jump right into explaining the Mormon religion in Korean, with no hand-holding, and they are relatively long, about two pages each in small type with vocabulary lists that range from about 40 to 70 words each. If you average out the new vocabulary words to about 50 words for each reading and multiply that by 100 lessons, then you get a total of 5,000 vocabulary words. Wow! That is a lot of words for just one language book.  Here is the first line of the first paragraph of the first reading:

성신  

아담과 이브가 에덴 동산을 떠난 후, 그 들은 땅을 경작하기 시작했고 살아 나가기 위해서 여러 가지 일을 행해야 했다. 

There is no translation for the reading, so I will translate the first sentence here:

The Holy Spirt

After Adam and Eve left the Garden of Eden, they had to start farming the land and doing various things to survive. 

I had always been curious about this book but had never read or heard any real description of it, so when I saw a used copy selling online for only $4.06 with free shipping, I bought it. As for the title of the book, "White Field Korean," I assume "White Field" (백전 白田) was Bruce Grant's Korean name or pen name.