Some documents are not intended for the general public to see. In John’s time, if a scroll was intended only for a particular reader, the knot on the strings holding it closed was encased in wax, perhaps with a mark unique to the sender pressed into the wax. Only the legitimate addressee was authorized to open the seals (as is true for us today with an envelope), and he could immediately determine whether someone had tampered with the seal.
1 Then I saw in the right hand of him who was seated on the throne a scroll written within and on the back, sealed with seven seals.