Translation
so that no one
would be able to buy or sell if he were not one of those having the mark
which is the name
of THE BEAST
or the number of his name.
Paraphrase
The result would be that no one would be able to buy or sell if he were not one of those having the clear indication of his allegiance to
the reputation and inner qualities of THE FEROCIOUS CREATURE, or
a summary of who he (the Beast) is.