Q: As I have a great interest in the Book of Revelation, I was very interested in the following statement contained in a Jewish history book: “For the Judaean in Persia ... the Torah was a book with seven seals.” What is the meaning or significance of “seven seals”?
A: The fact of something being closed with seven seals basically emphasizes the secrecy of the document. It generally means something that was divinely decreed, but, nevertheless, hidden in mystery form. The usage of the expression “seven seals” stresses the extreme nature of the mysteries contained inside.
That emphasis is clear in the quotation you mention: “... the Torah was a book with seven seals” for the Judaean(s) in Persia because these Jews had become accustomed to Aramaic script, and, so, were unable to read the Old Hebrew script of the Torah. Until it could be rewritten in Aramaic script, then, the Torah was sealed with seven seals, meaning that its mysteries (content) could not be comprehended.
By the same token, the scroll of Revelation five was tightly closed with seven seals, its content a complete mystery until is was made available in Revelation 6-22. The concept of hidden content fits well with Jewish usage of the terminology, as the quote you cite concurs.
I might also add that under Roman law, scrolls were required to be sealed seven times, and it is known that the scrolls of Roman Emperors, such as Augustus and Vespasian, were sealed seven times. The point of similarity, here, is that the content would be a secret or a mystery until it was opened following the death of the Emperor. Some of this also seems to apply to Revelation five: Only the Lion-Lamb was qualified to open the seven-sealed scroll, as only God the Son had shed His blood and died; this seems to be emphasized in the statement describing the Lion-Lamb as “though He had been slain.” Though Roman practice may have been of some influence in John's writing, I think the Jewish background fits it better. However, it is possible that John used both concepts here.