I think the *be* in this phrase might be the [lexical be][1], which is mostly used in negative constructions now, but I understand was more widely used in centuries past. 

    In CGEL page 114 has info related to lexical be usage, including examples:

    Lexical be

    This is found with why + do and with if:

    [63]

        i.a. Why don't you be more tolerant?

        i.b. Why doesn't he be more tolerant?

        ii.a. If you don't be quick you'll lose.

        ii.b. If he doesn't be quick he'll lose.

        iii.a. % If you be quick you'll win. -- (grammatical in some dialects only)
        iii.b. * If he be / bes quick he'll win. -- (ungrammatical)




  [1]: http://ell.stackexchange.com/a/44299/9675