There are two noteworthy things about this book.
It, and the Impossible to Lie book, were the only ones so important that a pocket deluxe edition was made (I have them).
Second, in the famous chart on page 35, the last entry in the Chart of Significant Dates is:
1975 End of 6th 1,000-year day of man's existence (in early autumn).
Right above this entry is:
1966 Book Life Everlasting-in Freedom of the Sons of God to be released Saturday, June 25, 1966.
A book so important that it itself is in the Chart of Significant Dates of mankind's history doesn't even a few years later make it into the WT index.