Why do I have to show passport/ID for payroll in Poland?

I HAVE APPLIED FOR A JOB,MY PASSPORT IS OUT OF DATE,I LOST MY ID 3 YEARS AGO,THE COMPANY THAT TOOK ME ON SAID I CANNOT BE PUT ON THE PAYROLL UNTIL I PRODUCE AN UP TO DATE PASSPORT.I DO HAVE THE WRS CERTIFICATE.WHY DO I HAVE TO SHOW ID/PASSPORT?

So they know you're you.

Because ... it's the law? How did you 'lose' your id and let your passport go out of date anyway? Is life a big challenge for you?