From the practically incoherent book The Finished Mystery, a commentary on the Book of Revelation and a compilation of Charles Russell's teachings after he died, page 134*:
7:9. After this, I beheld, and lo, a great multitude.— When the Apostle tells us In 2 John 8, "Look to yourselves that ye lose not those things which we have wrought, but that ye receive a full reward," he Is teaching that a Heavenly reward may be gained that is not as full as If a course more pleasing to the Heavenly Father Is pursued.
Instead of teaching that the saved of our race will all be saved to the same thing, the Scriptures show two degrees or kinds of Heavenly salvation, and two degrees or kinds of earthly salvation. In the second chapter of Genesis the stream which went forth from the Garden of Eden was divided Into four parts. This is a Scriptural recognition of the fact that from Adam, the original fountain of life, will flow four streams: The Little Flock, who are to sit down with Christ In His Throne; the Great Company, who are to stand before the Throne, having the palms of martyrdom but without the crowns of glory; the Ancient Worthies, the Jewish fathers, Abraham, Isaac, Jacob, Daniel, etc., who are to be made princes in all the earth; and the world of mankind, who will constitute the subjects of the Kingdom over which the Ancient Worthies will rule. The same lesson Is taught in the division of the Levltes into four camps, each located on a different side of the Tabernacle. (Num. 3:15; F128, 129.) It Is also taught In the Apostle's statement In 2 Tim. 2:20, that In God's great House there will ultimately be found four classes of vessels to His praise.
*Note: If you find a PDF of The Finished Mystery use the scripture cited in Revelation as a guide instead of page numbers as the numbers differ in different versions of the book.