And when I looked, behold, an hand was sent unto me; and, lo, a roll of a book was therein; A hand was sent - Here the hand signifies not only the instrument of conveyance, but an emblem of the Divine power, which the hand of God always signifies.
A roll of a book - מגלת שפר megillath sepher. All ancient books were written so as to be rolled up; hence volumen, a volume, from volvo, I roll.