http://www.strictlygenteel.co.uk/harp/harptitle.html
Some amazing publications online.
Just one example of the spiritual food at the proper time that earned JWs appointment by Christ as the FDS in Spring 1919. Chapter 9 "Our Lord's Return is very interesting. This, and Studies in the Scriptures, also available free online are the teachings that won the organisation its appointment.
For any who doubt the authenticity, I have old hardcopy editions at home. I have the 1921 edition, for example, of Rutherford's Harp of God.