What is the significance of the quote from The Crucible, which is listed below?"They [the books] must be [heavy]; they are weighted with authority."

This statement from The Crucible was
made by Reverend Hale as he arrived in Salem.  These books are the reference books Hale
will use to determine whether or not Salem has, in fact, been visited by witches. 
Reverend Parris makes a rather off-hand comment about how heavy they are as he helps
Hale carry them to his house.  Reverend Hale sees nothing to joke about and replies with
the quote you cite above.  This statement has significance in several
ways.

First, though these sober Puritans were unlikely to
be too frivolous in such matters, Hale's statement reminded them all that witchcraft
(and thus the presence of the Devil and his spirits) was no joking matter.  Second, Hale
was a learned man who had studied these tomes carefully, and the fact that he had been
sent for was an indication that the Devil may very well have set up shop in Salem.  He
was the authority, based on those books, which were another authority.  Third, if these
books proved the existence of witchery they carried the spiritual weight and authority
of law.  The books were the authority of the law in terms of these matters; and the
keeper (and interpreter) of the books, Hale, was their
authority.