• There is only one current package.

  ...
  package Foo;
  ...
  package Bar;
  ...
  [download]

• The program can be in multiple lexical scopes at a time, as long as they are nested.

  {
     my $foo;
     {
        my $bar;
        ...
     }
     ...
  }
  [download]

• The lexical state is cleared when the lexical scope is exited.

  for (1..2) {
     my $x;        # New variable each time.
     print($x);
  }
  [download]

• The package state is persistent.

  package Foo;
  use Carp qw( carp );
  carp('One');
  
  package Bar;
  ...
  
  package Foo;
  carp('Two');
  [download]

• Since the lexical state ceases to exist when exited, it cannot be referenced from the outside.

• The package state can be referenced from the outside

  package Foo;
  use Carp qw( carp );
  carp('One');
  
  package Bar;
  Foo::carp('Two');
  
  package Foo;
  carp('Three');
  [download]

The use directive itself doesn't know or care about scope. It's all about the code in the import function of the loaded .pm.

use pragma; changes bits in a lexically-scoped compiler variable.
use Module qw( function ); creates a function in the current package.