E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
White Stone (Rev. ii. 17).
To him that overcometh will I give . . a white stone; and in the stone a new name [is] written which no man knoweth saving he that receiveth it [i.e. the stone]. In primitive times, when travelling was difficult for want of places of public accommodation, hospitality was exercised by private individuals to a great extent. When the guest left, the host gave him a small white stone cut in two; on one half the host wrote his name, and on the other the guest; the host gave the guest the half containing his [hosts] name, and vice versâ. This was done that the guest at some future time might return the favour, if needed. Our text says, I will give him to eat of the hidden mannai.e. I will feed or entertain him well, and I will keep my friendship, sacred, inviolable, and known only to himself.