This is what the Matthew Henry commentary has to say:
"III. We have the conclusion of this epistle, where, after the usual demand of universal attention, there is the promise of great favour to those that overcome. They shall eat of the hidden manna, and have the new name, and the white stone, which no man knoweth, saving he that receiveth it, v. 17. 1. The hidden manna, the influences and comforts of the Spirit of Christ in communion with him, coming down from heaven into the soul, from time to time, for its support, to let it taste something how saints and angels live in heaven. This is hidden from the rest of the world�a stranger intermeddles not with this joy; and it is laid up in Christ, the ark of the covenant, in the holy of holies. 2. The white stone, with a new name engraven upon it. This white stone is absolution from the guilt of sin, alluding to the ancient custom of giving a white stone to those acquitted on trial and a black stone to those condemned. The new name is the name of adoption: adopted persons took the name of the family into which they were adopted. None can read the evidence of a man's adoption but himself; he cannot always read it, but if he persevere he shall have both the evidence of sonship and the inheritance."
http://www.ccel.org/ccel/henry/mhc6.xxvii.iii. html
Revelation is so fascinating.