The purpose of the forerunner-books is to mediate the recognition of the great uniform guidance from the Light, through which mankind was meant to be carefully guided step by step over thousands of years to the recognition of the Light.
This was the task of the Forerunners:

Their teachings were long ago willed by God, exactly adapted to their peoples and countries, and formed according to their spiritual maturity at the time.

The writings about the destinies of these Forerunners show clearly, free from prejudices and distortions, their earth-lives, their growing and working in the service of the Light, and their fierce inner struggles just as they were; for the time has come when in the closing of the cycle of all happenings they bear witness to the Word of Truth which has ever again been distorted by mankind.

The unprejudiced reader will perceive how new spiritual paths open here for him personally.