sql> create table test (
   2       test_id integer
   3     , constraint pk_test primary key (test_id)
   4   )
   5   /

Table created.

sql> create or replace package pkg_test as
   2     function insertEnable return boolean;
   3     pragma restrict_references (insertEnable, wnds, wnps);
   4     procedure insertTest(p_test_id integer);
   5   end;
   6   /

Package created.

sql> create or replace package body pkg_test as
   2     v_insertEnable boolean := false;
   3   
   4     function insertEnable return boolean as
   5     begin
   6       return v_insertEnable;
   7     end;
   8   
   9     procedure insertTest(p_test_id integer) as
  10     begin
  11       v_insertEnable := true;
  12       insert into test(test_id) values (p_test_id);
  13       v_insertEnable := false;
  14     exception when others then
  15       v_insertEnable := false;
  16       raise;
  17     end;
  18   end;
  19   /

Package body created

sql> 
sql> create or replace trigger tbi_test
   2   before insert on test
   3   begin
   4     if not pkg_test.insertEnable then
   5       raise_application_error(- 20001 , 'Call pkg_test.insertTest for insert into test');
   6     end if;
   7   end;
   8   /

Trigger created

sql> insert into test (test_id) values ( 1 );

insert into test (test_id) values ( 1 )

ORA- 20001 : Call pkg_test.insertTest for insert into test
ORA- 06512 : at  "DAN.TBI_TEST" , line  3 
ORA- 04088 : error during execution of trigger 'DAN.TBI_TEST'

sql> exec pkg_test.insertTest( 1 );

PL/SQL procedure successfully completed